Methods, systems, and vehicles with electromechanical variable transmission

ABSTRACT

A method of operating a first motor/generator and a second motor/generator in a vehicle drive includes operating the vehicle drive in a first operating mode and a second operating mode, the first operating mode including operating the first motor/generator as a generator and operating the second motor/generator as a motor, the second operating mode including operating both the first motor/generator as a generator and the second motor/generator as a generator when a first power generation capability associated with the first motor/generator is below a first threshold level, the first motor/generator and the second motor/generator providing electrical power to the DC bus without doing either of (a) providing electrical power to an energy storage device or (b) consuming electrical power from an energy storage device.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/155,224, filed Jan. 14, 2014, which claims the benefit of U.S.Provisional Patent Application Nos. 61/785,479, filed Mar. 14, 2013, and61/783,132, filed Mar. 14, 2013, all of which are incorporated herein byreference in their entireties.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.N00014-09-C-0061 awarded by the Office of Naval Research. The Governmenthas certain rights in this invention.

BACKGROUND

The present disclosure relates generally to the field of transmissionsfor vehicles. More specifically, the present disclosure relates to thefield of electromechanical infinitely variable transmissions forvehicles.

SUMMARY

One exemplary embodiment relates a method of operating a firstmotor/generator and a second motor/generator in a vehicle drive, thefirst motor/generator electrically coupled to the second motor/generatorby a DC bus and the vehicle drive configured to propel a vehicle. Themethod includes operating the vehicle drive in a first operating modeby: operating the first motor/generator as a generator, wherein thefirst motor/generator provides electrical power to the DC bus tomaintain a first voltage on the DC bus when operated as a generator, andwherein the first motor/generator provides all of an electrical powerrequired by the second motor/generator and an electrical power requiredto offset electrical power losses; and operating the secondmotor/generator as a motor, wherein the second motor/generator consumeselectrical power from the DC bus when operated as a motor, and wherein asum of the electrical power provided by the first motor/generator, theelectrical power losses, and the electrical power consumed by the secondmotor/generator is zero; wherein the first motor/generator provideselectrical power to the DC bus and the second motor/generator consumeselectrical power from the DC bus without doing either of (a) providingelectrical power to an energy storage device or (b) consuming electricalpower from an energy storage device. The method also includes operatingthe vehicle drive in a second operating mode by: operating both thefirst motor/generator as a generator and the second motor/generator as agenerator when a first power generation capability associated with thefirst motor/generator is below a first threshold level, wherein thefirst motor/generator and the second motor/generator provide electricalpower to the DC bus to maintain a second voltage on the DC bus whenoperated as generators, and wherein the first motor/generator and thesecond motor/generator provide all of the electrical power required tooffset electrical power losses; wherein the first motor/generator andthe second motor/generator provide electrical power to the DC buswithout doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.

Another exemplary embodiment relates to a method of operating a firstmotor/generator and a second motor/generator in a vehicle drive, thefirst motor/generator electrically coupled to the second motor/generatorby a DC bus and the vehicle drive configured to propel a vehicle. Themethod includes operating the vehicle drive in a first operating modeby: operating the first motor/generator as a generator, wherein thefirst motor/generator provides electrical power to the DC bus tomaintain a first voltage on the DC bus when operated as a generator, andwherein the first motor/generator provides all of an electrical powerrequired by the second motor/generator and an electrical power requiredto offset electrical power losses; and operating the secondmotor/generator as a motor, wherein the second motor/generator consumeselectrical power from the DC bus when operated as a motor, and wherein asum of the electrical power provided by the first motor/generator, theelectrical power losses, and the electrical power consumed by the secondmotor/generator is zero; wherein the first motor/generator provideselectrical power to the DC bus and the second motor/generator consumeselectrical power from the DC bus without doing either of (a) providingelectrical power to an energy storage device or (b) consuming electricalpower from an energy storage device. The method also includes operatingthe vehicle drive in a second operating mode by: operating both thefirst motor/generator as a generator and the second motor/generator as agenerator when the electrical power losses are greater than theelectrical power provided by the first motor/generator, wherein thefirst motor/generator and the second motor/generator provide electricalpower to the DC bus to maintain a second voltage on the DC bus whenoperated as generators, and wherein the first motor/generator and thesecond motor/generator provide all of the electrical power required tooffset electrical power losses; wherein the first motor/generator andthe second motor/generator provide electrical power to the DC buswithout doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.

Another exemplary embodiment relates to a system for operating a firstmotor/generator and a second motor/generator in a vehicle drive, thefirst motor/generator electrically coupled to the second motor/generatorby a DC bus and the vehicle drive configured to propel a vehicle, thesystem including a processing circuit. The processing circuit isconfigured to operate the vehicle drive in a first operating mode by:operating the first motor/generator as a generator, wherein the firstmotor/generator provides electrical power to the DC bus to maintain afirst voltage on the DC bus when operated as a generator, and whereinthe first motor/generator provides all of an electrical power requiredby the second motor/generator and an electrical power required to offsetelectrical power losses; operating the second motor/generator as amotor, wherein the second motor/generator consumes electrical power fromthe DC bus when operated as a motor, and wherein a sum of the electricalpower provided by the first motor/generator, the electrical powerlosses, and the electrical power consumed by the second motor/generatoris zero; wherein the first motor/generator provides electrical power tothe DC bus and the second motor/generator consumes electrical power fromthe DC bus without doing either of (a) providing electrical power to anenergy storage device or (b) consuming electrical power from an energystorage device. The processing circuit is also configured to operate thevehicle drive in a second operating mode by: operating both the firstmotor/generator as a generator and the second motor/generator as agenerator when a first power generation capability associated with thefirst motor/generator is below a first threshold level, wherein thefirst motor/generator and the second motor/generator provide electricalpower to the DC bus to maintain a second voltage on the DC bus whenoperated as generators, and wherein the first motor/generator and thesecond motor/generator provide all of the electrical power required tooffset electrical power losses; wherein the first motor/generator andthe second motor/generator provide electrical power to the DC buswithout doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of drive train for a vehicle according to anexemplary embodiment.

FIG. 2 is a detailed schematic view of the drive train shown in FIG. 1according to an exemplary embodiment.

FIG. 3 is a schematic diagram of a control system for the drive trainshown in FIG. 1 according to an exemplary embodiment.

FIG. 4 is a flow diagram of a process for controlling the propulsion ofthe vehicle, according to an exemplary embodiment.

FIG. 5 is a schematic view of a planetary gear set for the vehicle,according to an exemplary embodiment.

FIG. 6 is a flow diagram of a process for choosing whether thetransmission is input-coupled and output-coupled, according to anexemplary embodiment.

FIG. 7 is a chart 700 describing whether the transmission isinput-coupled or output-coupled, according to an exemplary embodiment.

FIG. 8 is a plot describing whether the transmission is input-coupled oroutput-coupled is shown, according to an exemplary embodiment.

FIGS. 9A-9C are schematic diagrams of the operations of theelectromagnetic devices EM1, EM2, according to exemplary embodiments.

FIG. 9A is a schematic diagram of electromagnetic device EM1 ingenerating mode and EM2 in motoring mode, according to an exemplaryembodiment.

FIG. 9B is a schematic diagram of electromagnetic device EM2 ingenerating mode and EM1 in motoring mode, according to an exemplaryembodiment.

FIG. 9C is a schematic diagram of electromagnetic devices EM1 and EM2 ingenerating mode, according to an exemplary embodiment.

FIG. 10 is a flow diagram of a process for choosing voltage mode andtorque mode for electromagnetic devices EM1 and EM2, according to anexemplary embodiment.

FIG. 11 is a chart of operational modes of electromagnetic devices EM1,EM2, according to an exemplary embodiment.

FIG. 12 is a chart for determining whether electromagnetic devices EM1,EM2 are motoring or generating, according to an exemplary embodiment.

FIG. 13 is a plot of simulated output power available as function ofengine speed, according to an exemplary embodiment.

FIG. 14 is a process for calculating engine speed, according to anexemplary embodiment.

FIG. 15 is a process for operating a voltage machine using closed loopcontrol is shown, according to an exemplary embodiment.

FIG. 16 is a process for determining a torque command for theelectromagnetic device in torque mode, according to an exemplaryembodiment.

FIG. 17 is a chart of speed constraints for engine E1, theelectromagnetic device in voltage mode, and the electromagnetic devicein torque mode, according to an exemplary embodiment.

FIGS. 18A-18D are plots of simulated operation of vehicle V1, accordingto exemplary embodiments.

FIG. 18A is a plot of simulated vehicle speed as a function of time,according to an exemplary embodiment.

FIG. 18B is a plot of simulated engine speed and speeds ofelectromagnetic devices EM1, EM2, according to an exemplary embodiment.

FIG. 18C is a plot of simulated engine torque and torques of theelectromagnetic devices EM1, EM2, according to an exemplary embodiment.

FIG. 18D is a plot of simulated power of the electromagnetic devicesEM1, EM2, according to an exemplary embodiment.

FIG. 19A is a block diagram of a vehicle controller, according to anexemplary embodiment.

FIG. 19B is a more detailed block diagram of the powerflow controller ofFIG. 19A, according to an exemplary embodiment.

FIG. 19C is a detailed diagram of communications between the powerflowcontroller of FIG. 19A and certain vehicle systems, according to anexemplary embodiment.

DETAILED DESCRIPTION

Drive Train

Referring to FIG. 1, a schematic view of a drive train for a vehicle V1is shown according to an exemplary embodiment. The vehicle V1 may be awork or commercial vehicle, a military vehicle, or any other type ofvehicle.

According to an exemplary embodiment, the drive train includes an engineE1 coupled to a transmission T1. The vehicle V1 also includes a firstelectromagnetic device EM1 coupled to the transmission T1 and a secondelectromagnetic device EM2 coupled to the transmission T1. The vehicleV1 also includes at least one drive axle (such as, e.g., rear axle RA1and/or front axle FA1) coupled to the transmission T1.

According to an exemplary embodiment, the engine E1 is configured toprovide rotational mechanical energy to the transmission T1. The engineE1 may be any source of rotational mechanical energy which is derivedfrom a stored energy source such as a liquid or gaseous fuel. Examplesare an internal combustion engine (such as a gas, natural gas, or dieselpowered engine), turbine, fuel cell, electric motor or any other type ofmotor capable of providing rotational mechanical energy to thetransmission T1. According to one exemplary embodiment, the engine E1 isa twelve liter diesel engine capable of providing approximately 400 to600 horsepower, 400-1500 ft-lbs of torque, and has a rotational speed ofapproximately 0 to 2100 rpm. According to one exemplary embodiment, theengine E1 is operated at a relatively constant speed (such as, e.g.,1600 rpm) to maximize fuel efficiency.

According to an exemplary embodiment, the electromagnetic devices EM1,EM2 are electric motor/generator devices that are capable of providingrotational electrical energy (as an electric motor) and/or capable ofproducing electrical power (as a generator). According to one exemplaryembodiment, the electromagnetic devices EM1, EM2 provide electric powerto one another, depending on the specific mode of operation of thevehicle V1. For example, the first electromagnetic device EM1 may beoperated as a generator to provide electric power to the secondelectromagnetic device EM2. Alternatively, the second electromagneticdevice EM2 may be operated as a generator to provide electric power tothe first electromagnetic device EM1.

According to one exemplary embodiment, the first electromagnetic deviceEM1 and the second electromagnetic device EM2 may be the same (orsimilar) to one another. However, according to other exemplaryembodiments, the first electromagnetic device EM1 and the secondelectromagnetic device EM2 may be sized differently as required by aparticular application. According to one exemplary embodiment, theelectromagnetic devices EM1, EM2 are each capable of providing up toapproximately 300 horsepower and 1300 ft-lbs of torque and are capableof rotational speeds from approximately −6,000 to 6,000 rpm (i.e., bothforward and reverse from 0 to 6,000 rpm).

According to an exemplary embodiment, the transmission T1 is coupled toat least one drive axle of the vehicle V1 (such as, e.g., rear axle RA1and/or front axle FA1 as shown in FIG. 1). According to one exemplaryembodiment, both the rear axle RA1 and the front axle FA1 are driven bythe transmission T1. According to other exemplary embodiments, only oneof the axles may be driven by the transmission T1. According to yetanother exemplary embodiment, additional axles (e.g., such as additionalrear axles not shown) may be driven by the transmission T1. According toan exemplary embodiment, each of the axles are coupled to thetransmission via a differential gear set (such as, e.g., reardifferential RD1 and/or front differential FD1 shown in FIG. 1). Eachaxle is configured to drive (i.e., provide rotational energy to) one ormore wheels/tires to propel (e.g., move, push, drive etc.) the vehicleV1.

Referring now to FIG. 2, a detailed schematic view of the drive trainfor the vehicle V1 is shown according to exemplary embodiment. As shownin FIG. 2, the transmission T1 includes two planetary gear sets.According to an exemplary embodiment, the transmission T1 includes afirst planetary gear set P1 and a second planetary gear set P2. A thirdplanetary gear set P3 is provided as a torque divider (e.g., 30% torqueto the front and 70% torque to the rear) if both the front and rearvehicle axles are powered.

According to one exemplary embodiment, the first planetary gear set P1is configured as a power split device or power splitting planetary gearset, the second planetary gear set P2 is configured as a gear reductionand/or torque amplification device, and the third planetary gear set P3is configured as a torque proportioning device. As shown in FIG. 2, thefirst planetary gear set P1 is coupled to the engine E1, the firstelectromechanical device EM1, the second electromechanical device EM2(via the second planetary gear set P2), and to gear G5. The secondplanetary gear set P2 is also coupled to the gear G5 (via gears G13,G14, G15, clutch C2 and shaft S6).

As shown in FIG. 2, the engine E1 is coupled to a clutch C3 that isconfigured to selectively rotationally engage/disengage the engine E1with the transmission T1. The clutch C3 may be any type of clutchcapable of rotationally fixing the engine E1 to the transmission T1.When the clutch C3 is engaged, the engine E1 is coupled to a shaft S1. Agear G6 is coupled (e.g., rotationally fixed) to shaft S1 and engages agear G7 that is coupled (e.g., rotationally fixed) to a shaft S2. Thegear G7 in turn is coupled to the first planetary gear set P1 via theshaft S2.

As shown in FIG. 2, the first planetary gear set P1 comprises an annulusor ring gear G1 which is coupled to the shaft S2. As shown, the clutchC3, the gears G6 and G7, and the shaft S2 cooperate to permit engine E1to drive the ring gear G1. The ring gear G1 is engaged with at least oneplanetary gear G2 (e.g., one, two, three, four or more planetary gearsG2 that are coupled to one another (e.g., rotatably supported) by aplanetary gear carrier PGC1). The planetary gear(s) G2 are engaged witha sun gear G3 of the first planetary gear set P1 to couple the ring gearG1 to the sun gear G3.

The sun gear G3 is directly coupled to the first electromagnetic deviceEM1 by a shaft S3. The first electromagnetic device EM1 may be coupledto an optional brake B1 by a clutch C4. The clutch C4 may be any type ofclutch capable of rotationally fixing the first electromagnetic deviceEM1 to the brake B1. The effect of braking the first electromechanicaldevice EM1 is to fix or hold sun gear G3 without the need to applyelectrical energy to the first electromechanical device EM1 to cause thefirst electromechanical device EM1 to generate enough holding torque tohold the gear G3 from rotating.

According to an exemplary embodiment, the planetary gear carrier PGC1 iscoupled to a carrier gear G4. The carrier gear G4 is engaged with a gearG5. In the preferred embodiment of vehicle V1, the gear G5 is part ofthe third planetary gear set P3 used to divide the power from thetransmission T1 to the front and rear axles. In this embodiment, thegear G5 is coupled to the planetary gears of the third planetary gearset P3. If only a single axle is driven by the transmission T1, or adifferent transfer device is used to drive more than one axle, the thirdplanetary gear set P3 may not be necessary.

The carrier gear G4 is also coupled to the second planetary gear set P2by a shaft S5 (as will be described in more detail below).

Still referring to FIG. 2, the transmission T1 also includes a clutch C1that selectively rotationally engages/disengages the engine E1 to thesecond electromagnetic device EM2. The clutch C1 may be any type ofclutch capable of rotationally fixing the engine E1 to the secondelectromagnetic device EM2, such as a wet clutch.

As shown in FIG. 2, the clutch C1 is coupled to the engine E1 by theshaft S1. When the clutch C1 is engaged, the shaft S1 is coupled to agear G9. The gear G9 in turn is engaged with a gear G8 that is coupledto the second electromagnetic device EM2. Thus, when the clutch C1 isengaged, the engine is coupled to the second electromagnetic device EM2to allow the second electromagnetic device EM2 to be driven as agenerator (e.g., to provide electrical power to the firstelectromagnetic device EM1).

The electromagnetic device EM2 is also coupled to the second planetarygear set P2 by a shaft S4. The shaft S4 is connected to a sun gear G12of the second planetary gear set P2. The sun gear G12 is engaged with atleast one planetary gear G11 (e.g., one, two, three, four or moreplanetary gears G11 that are coupled to one another (e.g., rotatablysupported) by a planetary gear carrier PGC2). The planetary gear(s) G11in turn are engaged with an annulus or ring gear G10 to couple the sungear G12 to the ring gear G10.

According to an exemplary embodiment, the planet gear carrier PGC2 ofthe second planetary gear P2 is coupled to the carrier gear G4 (and theplanet gear carrier PGC1) of the first planetary gear set P1 by a shaftS5. Thus, the planet gear carrier PGC1 and the planet gear carrier PGC2are coupled to one another so that the second electromagnetic device EM2is coupled to the first planetary gear set P1 via the second planetarygear set P2.

The second electromagnetic device EM2 is also coupled to the thirdplanetary gear set P3 via the second planetary gear set P2. According toan exemplary embodiment, the ring gear G10 of the second planetary gearP2 is coupled to an output gear G13 that is engaged with an idler gearG14. The idler gear G14 in turn is engaged with a gear G15 that isselectively engaged/disengaged to the third planetary gear set P3 by aclutch C2 (via a shaft S6). The clutch C2 may be any type of clutchcapable of rotationally fixing the gear G15 to the shaft S6, such as awet clutch.

According to an exemplary embodiment, the third planetary gear set P3 isa torque proportioning device for the front and rear axles of thevehicle V1. Torque is delivered from the third planetary gear set P3 tothe front axle FA1 and/or the rear axle RA1 via shafts S7 and S8. Asdiscussed above, in other exemplary embodiments, the third planetarygear set P3 is not necessary when either the front axle FA1 or rear axleRA1 of the vehicle V1 is not driven by the transmission T1.

According to an exemplary embodiment, the transmission T1 is operated ina low speed mode (e.g., a vehicle speed of approximately 0-10 mph) byhaving the clutch C2 engaged and the clutch C1 disengaged. According toanother exemplary embodiment, the transmission T1 is operated in a highspeed mode (e.g., a vehicle speed of approximately 10-65 mph) by havingthe clutch C1 engaged and the clutch C2 disengaged. According to othervarious embodiments, the vehicle speeds in the low and high speed modesmay vary higher or lower.

According to an exemplary embodiment, an operator (e.g., driver) ofvehicle V1 may manually switch the transmission T1 from low speed modeto high speed mode or vice-versa. According to another exemplaryembodiment, the transmission T1 is automatically switched from low speedmode to high speed mode (and vice-versa) by a control system (see, e.g.,FIG. 3). The control system may include various operator inputs (suchas, e.g., desired vehicle speed, torque, traction, terrain, etc.) andalso various system inputs (such as, e.g., current vehicle speed, enginespeed, power, and torque, electromagnetic device speed, power, andtorque, etc.). As shown in FIG. 3, according to one exemplaryembodiment, the control system is configured to monitor and/or controlthe engine, the mode of the transmission, the first electromagneticdevice EM1, the second electromagnetic device EM2, the clutch C1, theclutch C2, and/or the clutch C3.

According to an exemplary embodiment, gears within the transmission T1are sized according to the specific application and desired performancecharacteristics of the vehicle V1. According to one exemplaryembodiment, the gears within the transmission T1 have tooth counts asshown in Table 1. However, according to other exemplary embodiments, thetooth counts of the gears may vary more or less than that shown.According to other exemplary embodiments, the engine E1, theelectromagnetic devices EM1 and EM2, the clutches C1-C4, and the shaftsS1-S8 may all vary according to the specific application and desiredperformance characteristics of the vehicle V1.

TABLE 1 Gear # Tooth Count Gear 1 81 Gear 2 24 Gear 3 33 Gear 4 77 Gear5 77 Gear 6 49 Gear 7 50 Gear 8 55 Gear 9 74 Gear 10 64 Gear 11 19 Gear12 26 Gear 13 28 Gear 14 47 Gear 15 82

It should be noted that references to “front,” “rear,” “top,” and “base”in this description are merely used to identify various elements as areoriented in the FIGS., with “front” and “rear” being relative to theenvironment in which the device is provided.

For the purpose of this disclosure, the term “coupled” means the joiningof two members directly or indirectly to one another. Such joining maybe stationary or moveable in nature. Such joining may be achieved withthe two members or the two members and any additional intermediatemembers being integrally formed as a single unitary body with oneanother or with the two members or the two members and any additionalintermediate members being attached to one another. Such joining may bepermanent in nature or may be removable or releasable in nature.

It is important to note that the construction and arrangement of theelectromechanical variable transmission as shown in the variousexemplary embodiments is illustrative only. Although only a fewembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (for example, variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited in the claims.For example, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. The order or sequence of any processor method steps may be varied or re-sequenced according to alternativeembodiments. Other substitutions, modifications, changes and omissionsmay also be made in the design, operating conditions and arrangement ofthe various exemplary embodiments without departing from the scope ofthe present embodiments.

Control Strategy

The components of vehicle V1 (e.g., transmission T1, engine E1,electromagnetic devices EM1, EM2, etc.) may be controlled so an operatorof the vehicle can propel the vehicle as desired. The components ofvehicle V1 may be configured to deliver the power requested by theoperator to the wheels of the vehicle. In some embodiments, vehicle V1may be advantageously propelled in a fuel-efficient manner. In someembodiments, vehicle propulsion may also be accomplished whilemaintaining engine E1 and electromagnetic devices EM1, EM2 withinacceptable operating speeds. In some embodiments, electromagneticdevices EM1, EM2 may generate and use electrical power without an energystorage device. In some embodiments, power balance may be advantageouslymaintained between EM1 and EM2.

Referring to FIG. 4, a flow diagram of a process 400 for controlling thepropulsion of the vehicle is shown, according to an exemplaryembodiment. Process 400 may be implemented by a control system, such ascontrol system 300 (FIG. 3), or a vehicle controller, such as vehiclecontroller 1902 (FIG. 19A). The control system and/or vehicle controllermay be configured to receive inputs from an operator of the vehicle. Thecontrol system and/or vehicle controller may be further configured todetermine appropriate operating conditions for the engine,electromagnetic devices, transmission, and other components of thevehicle based on the operator's inputs. The control system and/orvehicle controller may be further configured to output commands tovarious components (e.g., engine, electromagnetic devices, clutches,etc.) of the vehicle based on the operating conditions determined to beappropriate. One or more of the steps of process 400 may be more fullydescribed in the discussion of process 1400 (FIG. 14), process 1500(FIG. 15), and/or process 1600 (FIG. 16).

Process 400 includes determining the current status of the vehicle andits components (402). The current status may be received and/ordetermined by powerflow controller 1904 of vehicle controller 1902 (FIG.19A). Determining the current status of the vehicle includes measuringinputs from a vehicle operator as to the desired operating state of thevehicle (404). Inputs may include shifter position (e.g., reverse,neutral, drive, etc.), throttle (based on, e.g., accelerator pedalsensor), brake, etc. Determining the current status of the vehicle alsoincludes determining current clutch status (406). In some embodiments, aclutch may be engaged or disengaged. The status of clutches (e.g.,clutches C1, C2 of FIG. 2) may determine the configuration of thetransmission (e.g., output-coupled or input-coupled). Determining thecurrent status of the vehicle also includes measuring current enginespeed, electromagnetic device EM1 speed, electromagnetic device EM2speed, and vehicle speed (408). Speeds may be monitored by powerflowcontroller 1904 (FIG. 19A). Determining the current status of thevehicle also includes determining the electrical power to total powerratio (410). According to an exemplary embodiment, the ratio ofelectrical power to total power in the drive train may be equal to afunction of the engine speed and the vehicle speed.

Process 400 includes determining the configuration of the transmission(412). According to an exemplary embodiment, the transmission of thevehicle may be configurable in two modes. In some embodiments, anoutput-coupled (OC) mode may be used for low vehicle speeds (e.g.,approximately 0-10 mph), and an input-coupled (IC) mode may be used forhigh vehicle speeds (e.g., approximately 10-65 mph). The modes maydiffer at least in how components of the drive train, such as aplanetary gear set and an electromagnetic device, are coupled to eachother. A particular configuration may be chosen by engaging ordisengaging clutches, such as clutch C1 and clutch C2 of FIG. 2. Atransmission configuration may be chosen based on, e.g., maintaining theelectromagnetic devices at acceptable operating speeds, delivering thepower requested to the wheels of the vehicle, etc. Step 412 determineswhether the current clutch status (determined in step 406) should bechanged so the transmission is in a different configuration (i.e., fromIC or OC, or from OC to IC).

Process 400 includes operating the clutches to reach the desiredtransmission configuration (422). If a change of transmissionconfiguration is necessary (e.g., from output-coupled to input-coupled),then clutch statuses may change. According to an exemplary embodiment,clutch C1 may be engaged and clutch C2 may be disengaged when thetransmission is in input-coupled mode. In output-coupled mode, clutch C1may be disengaged and clutch C2 may be engaged. Commands to the clutchesmay be transmitted by powerflow controller 1904 of vehicle controller1902 (FIG. 19A).

Process 400 includes computing maximum power available at currentoperating conditions (414). The maximum power available may describe thepower that can be delivered to the wheels of the vehicle, based on inputfrom the vehicle operator (e.g., increasing throttle). The maximum poweravailable may be determined at least in part by transmission mode, andcurrent vehicle speed, engine speed, EM1 speed, and EM2 speed. Accordingto an exemplary embodiment, the maximum power available may vary foreach vehicle speed. For each vehicle speed, the maximum power availablemay vary for each engine speed and for each transmission mode. Accordingto an exemplary embodiment, powerflow controller 1904 of vehiclecontroller 1902 (FIG. 19A) may compute a collection or map of maximumpower at a variety of vehicle speeds, engine speeds, and transmissionconfigurations.

Process 400 includes computing the power desired by a vehicle operator(416). The proportion of available power desired by the operator may bedescribed by the throttle input. Throttle input may be measured by anaccelerator pedal sensor. For example, an operator may request maximumpower at 100% or full throttle (i.e., depressing the accelerator pedalto the greatest extent possible). The power desired by the operator maybe computed by multiplying the throttle input proportion (measured instep 404) by the maximum power available (computed in step 414).

Process 400 includes determining an optimum engine speed (424). Enginespeed may be determined based on the maximum power available (computedin step 414) and the power desired by the operator of the vehicle(computed in step 416). For example, if the current engine speed is toolow to provide the power requested, then engine speed may be increased.According to an exemplary embodiment, a range of engine speeds mayprovide the required power. A particular engine speed may be selectedfrom the range to advantageously maximize fuel economy. In someembodiments, the lowest speed in the range may be chosen for the enginespeed. In other embodiments, an engine speed may be selected in order tosatisfy a variety of constraints on the drive train (e.g., maintainingelectromagnetic devices EM1, EM2 within acceptable operating speeds).

Process 400 includes computing the required electrical power (418).According to an exemplary embodiment, power in the transmission may flowin two paths: electrical and mechanical. The phrase “electrical power”describes power in the drive train that flows through theelectromagnetic devices. Electrical power originates as mechanical powerfrom the engine and terminates as mechanical power at the transmission.In some embodiments, the electrical power can be calculated based on thetotal power (computed in step 416) and the electrical to total powerratio (determined in step 410). According to an exemplary embodiment,the portion of total power requested by the vehicle operator that iselectrical power can be computed by multiplying the total power by theelectrical to total power ratio. According to an exemplary embodiment,the electrical power required may be generated by one of theelectromagnetic devices EM1, EM2.

Process 400 includes determining the operational mode for theelectromagnetic devices EM1, EM2 (420). According to an exemplaryembodiment, EM1 and EM2 may either be in torque mode or voltage mode. Anelectromagnetic device in torque mode may be referred to as a torquemachine, and an electromagnetic device in voltage mode may be referredto as a voltage machine. Torque mode may describe the state of anelectromagnetic device that maintains a calculated torque at its output.Voltage mode may describe the state of an electromagnetic device thatmaintains power balance with the electromagnetic device in torque mode.The voltage machine may maintain a voltage on the DC bus between EM1 andEM2. The DC bus may be considered an electrical power transmissionsystem. In both torque mode and voltage mode, EM1 and EM2 may bemotoring (receiving electrical power from the other electromagneticdevice and providing mechanical power to the wheels of the vehicle) orgenerating (receiving mechanical power from the engine and providingelectrical power to the other electromagnetic device). In someembodiments, EM1 may be in voltage mode and EM2 may be in torque modefor low vehicle speeds. EM1 may be in torque mode and EM2 may be involtage mode for high vehicle speeds. When the vehicle is acceleratingfrom low vehicle speeds to higher vehicle speeds, step 420 determineswhether EM1 should switch to torque mode and whether EM2 should switchto voltage mode. According to an exemplary embodiment, EM1 may switchfrom voltage mode to torque mode when EM1 speed is less than a thresholdspeed. In some embodiments, EM2 may switch to voltage mode after thetransmission configuration has changed from output-coupled toinput-coupled.

Process 400 includes computing the torque required from theelectromagnetic device in torque mode (426). The torque may be computedby dividing the required electrical power (computed in step 418) by thespeed of the electromagnetic device (measured in step 408). Computationof the torque command is described in greater detail in the discussionof FIG. 16. The torque and speed of a given electromagnetic device maybe adjusted to so that it outputs the required power. For example, toachieve the required power, speed or torque or both may be increased.According to an exemplary embodiment, the power used or generated by thevoltage machine may be approximately equal to the power generated orused by the torque machine. The power may not be exactly equal becauseof ordinary electrical power losses. The torque computation may estimatethe power losses and select a torque that is consistent with theexpected electrical power flow in the drive train. Once the torque hasbeen computed, process 400 includes commanding the torque to the torquemachine (428).

Process 400 includes commanding the voltage machine to maintain powerbalance with the torque machine (430). The voltage machine may maintainpower balance with the torque machine by providing electrical power tothe torque machine (when the torque machine is motoring) or receivingelectrical power from the torque machine (when the torque machine isgenerating). The voltage machine may be controlled using closed loopcontrol on the voltage on the DC bus between the two electromagneticdevices. The closed loop control scheme is described in greater detailin the discussion of FIG. 15, below. The voltage machine may increase ordecrease voltage on the DC bus by increasing or decreasing its torque orspeed or both.

Transmission Configurations

According to an exemplary embodiment, the purpose of transmission T1 isto take power from engine E1 at the transmission's input shaft anddeliver the power to the transmission's output shaft for subsequentdelivery to the wheels of vehicle V1 for vehicle propulsion.

Referring to FIG. 5, a schematic view of a planetary gear set for thevehicle is shown, according to an exemplary embodiment. The planetarygear set P1 of FIG. 5 shows the component gears of the planetary gearset are coupled to an engine and two electromagnetic devices. One ormore of the elements of FIG. 5 may have similar structure and/orfunction as described with respect to the corresponding elements of FIG.2. FIG. 5 may not show or describe all of the elements and functions ofFIG. 2, and FIG. 2 may not show or describe all of the elements andfunctions of FIG. 5. The schematic view of FIG. 5 may omit intermediatecoupling details, such as intermediate planetary gear sets, gears,shafts, and clutches.

Planetary gear set P1 of FIG. 5 may be the same as or similar to theplanetary gear set P1 depicted in FIG. 2. Planetary gear set P1 may havea ring gear G1, planetary gear carrier PGC1, and sun gear G3. Asdiscussed in the description of FIG. 2, ring gear G1 may be coupled tosun gear G1 via at least one planetary gear (not shown in FIG. 5).According to an exemplary embodiment, the output of planetary gear setP1 may be coupled to planetary gear carrier PGC1.

The planetary gear set of FIG. 5 includes engine E1. According to anexemplary embodiment, engine E1 may be coupled to ring gear G1. In someembodiments, engine E1 may remain coupled to ring gear G1 regardless ofwhether vehicle V1 is in input-coupled or output-coupled mode (i.e.,regardless of the vehicle speed). In some embodiments, when thetransmission is input-coupled, the engine is selectively coupled to thesecond motor/generator via a second clutch (e.g., the input clutch). Insome embodiments, engine E1 is also uncoupled from the output of theplanetary gear set P1 when vehicle V1 is in input-coupled mode andoutput-coupled mode. Thus, engine speed is uncoupled from vehicle speedfor all vehicle speeds.

The planetary gear set of FIG. 5 includes electromagnetic device EM1.According to an exemplary embodiment, EM1 may be coupled to sun gear G3.At any given vehicle speed, EM1 speed increases (i.e., becomes morepositive) when engine speed increases. EM1 speed decreases when vehiclespeed increases. According to some embodiments, EM1 speed may bepositive at low vehicle speeds. As vehicle speed increases, EM1 speedbecomes more negative. As described in the discussion of FIG. 5, EM1switches from voltage mode to torque mode when EM1 speed is less (i.e.,more negative) than a threshold speed. EM1 speed may near a maximumspeed in the negative direction at high vehicle speeds. In order tomaintain EM1 speed below the maximum, engine speed may be increased,causing EM1 speed to become more positive. In some embodiments, EM1 mayremain coupled to engine E1 and the output of planetary gear set P1,regardless of whether vehicle V1 is in input-coupled or output-coupledmode (i.e., regardless of the vehicle speed).

The planetary gear set of FIG. 5 includes electromagnetic device EM2.According to an exemplary embodiment, EM2 may be selectively coupled tothe planetary gear carrier PGC1 of the first planetary gear set P1 andthe ring gear G1 of the first planetary gear set P1. According to anexemplary embodiment, EM2 may be coupled to planetary gear carrier PGC1,if the transmission is output-coupled, and ring gear G1, if thetransmission is input-coupled. When EM2 is output-coupled, EM2 iscoupled to the output of the planetary gear set P1, which is alsocoupled to planetary gear carrier PGC1. In some embodiments, EM2 iscoupled to the output of planetary gear set P2. In some embodiments,when the transmission is output-coupled, a first clutch (e.g., theoutput clutch) is configured to selectively engage the secondmotor/generator to the planetary gear carrier PGC1 of the firstplanetary gear set. In the discussion herein, EM2 may be described asbeing coupled to the output planetary gear set P1 because the outputs ofboth planetary gear sets are ultimately combined to propel the vehicle.EM2 speed may be proportional to vehicle speed when EM2 isoutput-coupled. According to an exemplary embodiment, the transmissionmay be coupled to output of the planetary gear set P1 at a high gearratio. Thus, EM2 speed may increase rapidly as vehicle speed increases.When the transmission is input-coupled, EM2 is coupled to engine E1,which is also coupled to ring gear G1. In some embodiments, when thetransmission is input-coupled, a second clutch (e.g., the input clutch)is configured to selectively engage the second motor/generator to theengine. EM2 speed may be proportional to engine E1 speed when thetransmission is input-coupled. According to an exemplary embodiment, thetransmission may be output-coupled at low vehicle speeds andinput-coupled at high vehicle speeds. The transmission may be configuredto switch between output-coupled mode and input-coupled mode dependingon EM2's speed, as described in the discussion of FIG. 6-8, below.

Referring again to FIG. 2, a more detailed schematic view of the drivetrain for vehicle V1 is shown, according to an exemplary embodiment. Oneor more of the elements of FIG. 2 may have similar structure and/orfunction as described with respect to the corresponding elements ofFIGS. 1 and 5. FIG. 2 may not show or describe all of the elements andfunctions of FIGS. 1 and 5, and FIGS. 1 and 5 may not show or describeall of the elements and functions of FIG. 2.

The drive train of FIG. 2 includes engine E1, and electromagneticdevices EM1, EM2. The drive train of FIG. 2 also includes transmissionT1. As described in the discussion of FIG. 2, engine E1 may be coupledto transmission T1 by clutch C3. According to an exemplary embodiment,engine E1 may be coupled to transmission T1 for all vehicle speeds.

In the embodiment of FIG. 2, transmission T1 is shown to includeplanetary gear set P1. Transmission T1 also includes clutch C1 andclutch C2. Clutch C1 may be described as an input clutch (or secondclutch), and clutch C2 may be described as an output clutch (or firstclutch). Whether clutch C1 and clutch C2 are engaged or disengaged maygovern the coupling of EM2 to planetary gear set P1. According to anexemplary embodiment, when transmission T1 is output-coupled, clutch C1is disengaged, clutch C2 is engaged, and EM2 is coupled to planetarygear carrier PGC1 of planetary gear set P1. When transmission T1 isinput-coupled, clutch C1 is engaged, clutch C2 is disengaged, and EM2 iscoupled to the ring gear G1 of planetary gear set P1.

According to an exemplary embodiment, the drive train of vehicle V1 maybe mechanically coupled in two configurations. The two configurationsmay be termed input-coupled and output-coupled. Input-coupled andoutput-coupled may specifically refer to how electromagnetic device EM2is coupled to one or more planetary gear sets of vehicle V1.“Input-coupled” and “output-coupled” are used to generally refer toconfiguration modes of vehicle V1 and/or transmission T1. In otherembodiments, the drive train of FIGS. 1 and 2 may be operable in oneconfiguration or more than two configurations.

According to an exemplary embodiment, the drive train of vehicle, suchas the drive train of vehicle V1 of FIGS. 1, 2, and 5 may be configuredto switch between output-coupled mode and input-coupled mode. Vehicle V1may switch from input-coupled mode to output-coupled mode and fromoutput-coupled mode to input-coupled mode depending on the operatingconditions of the vehicle. Relevant operating conditions may includevehicle speed and speed of electromagnetic device EM2. The vehicle mayswitch between output-coupled mode and input-coupled mode when EM2 speedis greater than a threshold.

Referring to FIG. 6, a flow diagram of a process 600 for choosingwhether the transmission is input-coupled or output-coupled is shown,according to an exemplary embodiment. Process 600 may be carried out bya control system, such as control system 300 (FIG. 3) and/or vehiclecontroller, such as vehicle controller 1902 (FIG. 19A). Though FIG. 6may refer to a specific electromagnetic device, e.g., EM2, as beingcoupled to a particular component of the drive train, both EM1 and EM2may be capable of operating as described below.

Process 600 includes operating the vehicle with the transmissionoutput-coupled (602). When the transmission is output-coupled, clutch C2is engaged and clutch C1 is disengaged (FIG. 2). Thus, EM2 is coupled toplanetary gear carrier PGC1 when the transmission is output-coupled.Planetary gear carrier PGC1 is also coupled to the output of planetarygear set P1, meaning EM2 is coupled to the output. In some embodiments,EM2 is coupled to the output of planetary gear set P2. The combinedoutputs of planetary gear sets P1 and P2 may provide mechanical power toone or more drive axles to propel the vehicle. When vehicle V1 isoutput-coupled, EM2 speed is directly proportional to the speed ofvehicle V1. According to an exemplary embodiment, the transmission maybe output-coupled when vehicle V1 speeds are low (e.g., 0-10 mph). Asvehicle V1 accelerates, EM2 speed increases.

According to an exemplary embodiment, EM2 may be in torque mode for lowvehicle speeds. Because EM2 speed increases as vehicle V1 speedincreases for low vehicle speeds, EM2 may have sufficient speed to beassume the role of voltage machine when required. As described in thediscussion of FIG. 10, EM2 switches from torque mode to voltage modewhen EM1 switches from voltage mode to torque mode (i.e., when EM1 speeddrops below a threshold speed such that it can no longer generatesufficient electrical power to maintain a DC bus voltage and supplyEM2's electrical power demand).

Process 600 includes determining if EM2 speed is above a threshold(604). Because EM2 is coupled to the output of planetary gear set P1,EM2 speed increases as the speed of vehicle V1 increases. EM2 speed mayreach a threshold speed beyond which it may not operate. The thresholdspeed may be a result of EM2's mechanical limitations and may varydepending on the electromagnetic device used. The upper threshold of EM2may be set by a manufacturer of the device. According to someembodiments, approximately 6000 RPM may be an upper threshold. Thetransmission may switch from output-coupled mode to input-coupled modeat or near the threshold speed.

Process 600 includes operating the vehicle with the transmissioninput-coupled if EM2 speed is above the threshold (606). When thetransmission is input-coupled, clutch C1 is engaged and clutch C2 isdisengaged (FIG. 2). Thus, EM2 is coupled to ring gear G1 when thetransmission is input-coupled. Ring gear G1 is also coupled to engineE1, meaning EM2 is coupled to engine E1. When vehicle V1 isoutput-coupled, EM2 speed is directly proportional to the speed ofengine E1. According to an exemplary embodiment, the transmission may beinput-coupled when vehicle V1 speeds are high (e.g., 10-65 mph). Becauseengine speed is decoupled from vehicle speed for all vehicle speeds, EM2speed is not directly affected by vehicle speed.

Process 600 includes operating the vehicle with the transmissionoutput-coupled if EM2 speed remains below the threshold (608).

Process 600 may describe whether the transmission is input-coupled oroutput-coupled when vehicle V1 is accelerating. A process similar toprocess 600 may occur when the vehicle is decelerating. According to anexemplary embodiment, the transmission will switch from input-coupledmode to output-coupled mode such that (a) EM2 speed goes through aminimal change; and (b) the vehicle gets sufficient torque to wheels.For example, if the vehicle is decelerating due to no throttle, theIC/OC switch will take place when EM2 speed before and after the modechange is approximately the same. This may be described as a zero or lowinertia shift because EM2 speed does not change or changes very little.

Referring to FIG. 7, a chart 700 describing whether transmission T1 isinput-coupled or output-coupled is shown, according to an exemplaryembodiment. Chart 700 describes more particularly the conditions whenthe transmission switches from output-coupled to input-coupled (or viceversa). Chart 700 includes vehicle operating statuses (702) and thecorresponding transmission configurations (704). The operationsdescribed in chart 700 may be implemented by powerflow controller 1904of vehicle controller 1902 (FIG. 19A). For example, if the vehiclestatus requires a switch from output-coupled mode to input-coupled mode,then powerflow controller 1904 may transmit a command to clutches C1, C2to reach the correct configuration.

Chart 700 shows that the transmission switches from output-coupled toinput-coupled when EM2 speed is greater than a threshold. As describedin the discussion of process 600 (FIG. 6), EM2 speed may reach athreshold speed beyond which it may not operate. Switching fromoutput-coupled to input-coupled configuration may advantageouslydecrease EM2 speed and advantageously prevent EM2 from operating at anexcessive speed.

Chart 700 shows that the transmission is in output-coupled configurationwhen the vehicle is in reverse. According to an exemplary embodiment,EM1 speed and EM2 speed may increase as vehicle speed, in reverse,increases. EM1 speed may increase because EM1 is coupled to the sun gearG3 of the planetary gear set P1 for all vehicle speeds. EM2 speed mayincrease because EM2 is coupled to the carrier gear G2 (output) of theplanetary gear set P1 when the transmission is output-coupled.

Chart 700 shows that the transmission will switch configurations (fromoutput-coupled to input-coupled) when the difference of EM2 speed inoutput-coupled mode and EM2 speed in input-coupled mode is above athreshold. In some embodiments, the threshold may be a fixed speed. Inother embodiments, the threshold may be dynamic. The threshold may varydepending on the throttle input proportion, i.e., the threshold may be afixed speed multiplied by the throttle input proportion. For example,threshold=200 RPM×50% throttle=100 RPM. In still other embodiments, adynamic threshold with positive or negative offsets may be used. Whenthe threshold is related to the throttle input, the shift fromoutput-coupled mode to input-coupled mode may be advantageously delayedto a higher vehicle speed. The transmission may remain output-coupledlonger when throttle input is high than if the vehicle were experiencinglesser throttle input. According to an exemplary embodiment, more poweris available to be delivered to the wheels when the transmission is inoutput-coupled mode (as described in the discussion of FIG. 13). Bydelaying the transition to input-coupled mode when the vehicle is underhigh tractive demand, more power is advantageously available to thevehicle for a longer period of time.

Powerflow controller 1904 of FIG. 19A may be configured to measure andmonitor EM2 speed. Powerflow controller 1904 may be further configuredto measure the difference of EM2 speed in output-coupled andinput-coupled modes. In order to so, powerflow controller 1904 maydetermine what the speed of EM2 would be were the transmissioninput-coupled, if the transmission is actually output-coupled.Similarly, if the transmission is actually input-coupled, then powerflowcontroller 1904 may determine what the speed of EM2 would be were thetransmission output-coupled.

Chart 700 shows that the transmission will switch configurations (frominput-coupled to output-coupled) when the difference of EM2 speed inoutput-coupled mode and EM2 speed in input-coupled mode is below athreshold. Depending on the embodiment, the threshold may be fixed ordynamic, with positive or negative offsets, as described above. Athreshold that is related to throttle input may be advantageous when avehicle is decelerating (due to, e.g., no throttle). In someembodiments, the transmission may switch from input-coupled mode tooutput-coupled mode so that the change in EM2 speed is minimal. Thisadvantageously minimizes the status change felt by a vehicle operator.In other embodiments, when the vehicle is experiencing high tractivedemands (and higher throttle), the transmission may shift tooutput-coupled mode sooner so that more power is available.

Referring to FIG. 8, a plot 800 describing whether the transmission isinput-coupled or output-coupled is shown, according to an exemplaryembodiment. Plot 800 represents, in graph-format, the conditions whenthe transmission switches from output-coupled mode to input-coupled mode(or vice versa). The x-axis of plot 800 is time. The y-axis of plot 800is wheel speed. Plot 800 shows an embodiment in which vehicle speedincreases linearly in time. In other embodiments, vehicle speed mayincrease non-linearly. For example, vehicle speed may increase with timein the manner shown in FIG. 18A. Plot 800 may depict relative (and notabsolute) conditions when a vehicle switches between input-coupled andoutput-coupled mode. Thus, the regions depicted in FIG. 8 apply evenwhen vehicle speeds increase non-linearly. The regions depicted in FIG.8 may also apply when vehicle speed is decreasing. The operationsdescribed in plot 800 may be implemented by powerflow controller 1904 ofvehicle controller 1902 (FIG. 19A). For example, if the vehicle statusrequires a switch from output-coupled mode to input-coupled mode, thenpowerflow controller 1904 may transmit a command to clutches C1, C2 toreach the correct configuration.

Plot 800 shows that the transmission is output-coupled for low vehiclespeeds (according to an exemplary embodiment, 0-10 mph) andinput-coupled for high vehicle speeds (according to an exemplaryembodiment, 10-65 mph). In various embodiments, low vehicle speeds andhigh vehicle speeds may refer to different speeds. Plot 800 shows that aregion of vehicle speeds when the transmission is transitioning betweeninput-coupled mode and output-coupled mode. As described in discussionof FIG. 6, the transmission may switch from output-coupled mode toinput-coupled mode when the speed of EM2 exceeds a threshold. The modeswitching region of plot 800 may correspond to this threshold.

In some embodiments, the transmission may switch configurations earlieror later (i.e., stay input-coupled or output-coupled longer or shorter).For example, under high tractive demands (when throttle input is high),the vehicle may stay output-coupled longer (when vehicle speed isincreasing). This may advantageously utilize the higher power availablewhen the transmission is output-coupled. As shown in plot 800, the“shift region to maximize performance” is at the end of the modeswitching region. When the vehicle is decelerating and experiencing hightractive demand, the transmission may transition to output-coupled modeearlier. As another example, under low tractive demands (when throttleinput is low), the vehicle may switch from output-coupled mode toinput-coupled mode early in the mode switching region (when vehiclespeed is decreasing). This may advantageously accomplish a low or zeroinertia shift in which EM2 speed in output-coupled mode is approximatelyequal to EM2 speed in input-coupled mode. When the vehicle isdecelerating and experiencing low tractive demand, the transmission maytransition to output-coupled mode later.

Electromagnetic Device Operations

The operations performed by electromagnetic devices EM1, EM2 may includemotoring and generating. While motoring, the electromagnetic device actsas an electric motor, converting electrical energy to mechanical energy.The electromagnetic device in motoring mode may receive electricalenergy from, e.g., another electromagnetic device (in generating mode),and provide rotational mechanical energy to, e.g., the transmission of avehicle to propel the vehicle. An electromagnetic device may be motoringwhen it is applying torque in the same direction as its speed. Whilegenerating, the electromagnetic device acts as an electric generator,converting mechanical energy to electrical energy. The electromagneticdevice in generating mode may receive rotational mechanical energy from,e.g., an internal combustion engine and provide electrical energy to,e.g., another electromagnetic device (in motoring mode). Anelectromagnetic device may be generating when it is applying torque inthe opposite direction as its speed. Electromagnetic devices EM1 and EM2may be configured to switch operations (i.e., from motoring togenerating and generating to motoring).

Referring to FIGS. 9A-9C, schematic diagrams of the operations ofelectromagnetic devices EM1, EM2 are shown, according to exemplaryembodiments. FIGS. 9A-9C include a DC bus or link between EM1 and EM2.The DC bus may be considered an electrical power transmission system.According to an exemplary embodiment, EM1 or EM2 may be configured tomaintain a voltage or a voltage range on the DC bus. FIGS. 9A-9C alsoincludes the output and/or input of mechanical power, which is indicatedby a thick line. FIGS. 9A-9C also include electrical power beingtransmitted between EM1 and EM2, which is indicated by line ofmedium-thickness. FIGS. 9A-9C also include electrical power losses,which are indicated by a thin line. Power losses arise from, e.g.,resistance of a conducting wire, and relate to the efficiency of theelectrical power path.

Referring to FIG. 9A, a schematic diagram of electromagnetic device EM1in generating mode and EM2 in motoring mode is shown, according to anexemplary embodiment. When it is generating, EM1 may receive mechanicalpower input from the engine. EM1, acting as a generator, converts themechanical power to electrical power. The voltage on the DC bus mayincrease when EM1 generates electrical power. EM2, acting a motor,coverts the electrical power to mechanical power. The voltage on the DCbus may decrease when EM2 uses the electrical power generated by EM1.EM2 transmits the mechanical power to the transmission to propel thevehicle. According to an exemplary embodiment, EM1 may be generating andEM2 may be motoring when the vehicle is accelerating from low vehiclespeeds (i.e., when the transmission is output-coupled). When thetransmission is output-coupled, EM2 is coupled to the planetary gearcarrier (output) of the planetary gear set.

Referring to FIG. 9B, a schematic diagram of electromagnetic device EM2in generating mode and EM1 in motoring mode is shown, according to anexemplary embodiment. EM2, as a generator, may receive mechanical powerfrom the engine and covert the mechanical power to electrical power.EM1, as a motor, may convert the electrical power to mechanical powerand transmit the mechanical power to the transmission of the vehicle.According to an exemplary embodiment, EM2 may be generating and EM1 maybe motoring when at high vehicle speeds (i.e., when the transmission isinput-coupled). EM1 is coupled to the sun gear of the planetary gear setfor all vehicle speeds.

Referring to FIG. 9C, a schematic diagram of electromagnetic devices EM1and EM2 in generating mode is shown, according to an exemplaryembodiment. Both EM1 and EM2, as generators, receive mechanical powerand convert it to electrical power. According to an exemplaryembodiment, the power generated may compensate for losses in theelectrical power path (and may not be used for, e.g., propelling thevehicle). This situation may arise when both EM1 and EM2 are at or nearzero power (i.e., torque×speed=0). The vehicle may be accelerating,decelerating, or coasting when both EM1 and EM2 are generating. Theseconditions are represented in the plot of FIG. 18D. As shown in FIG.18D, EM1 starts from negative power (generating) and goes through thezero power point to positive power (motoring). EM2 starts from positivepower (motoring) and goes through the zero power point to positive power(generating). The crossover over point is below the zero power line,indicating that both EM1 and EM2 are generating for a period of time. Inan ideal case, there was no electrical power loss. EM1 and EM2 would gothrough the zero power point simultaneously, and both EM1 and EM2 wouldnever be generating at the same time. However, because there areelectrical power losses, both EM1 and EM2 generate to overcome thelosses.

Power Balance

According to an exemplary embodiment, the drive train of vehicle V1 maybe configured to operate with electromagnetic devices EM1, EM2, and noadditional sources of electrical power. Additional sources of electricalpower include, e.g., a battery and other energy storage devices. Withoutan energy storage device, the electromagnetic devices EM1, EM2 operatein power balance. One of the electromagnetic devices may provide all ofthe electrical power required by the other electromagnetic device (aswell as the electrical power required to offset power losses). Theelectromagnetic devices EM1, EM2 may operate without doing either of (a)providing electrical power to an energy storage device or (b) consumingelectrical power from an energy storage device. The sum of theelectrical power produced or consumed by EM1, the electrical powerproduced or consumed by EM1, and electrical power losses is zero.According to the embodiment of FIGS. 1 and 2, two electromagneticdevices are shown. In other embodiments, three or more electromagneticdevices may be utilized.

According to some embodiments, the drive train of vehicle V1 may includean energy storage device, e.g., a battery. In such embodiments, thebattery may charged and recharged by an electromagnetic device that isgenerating power. The battery may supply the electromagnetic device thatis motoring the vehicle to propel the vehicle. In some embodiments, thebattery may always be utilized as part of the drive train. In otherembodiments, the battery may be used only when excess generated powermust be stored or excess power is required to motor the vehicle. In theembodiment of vehicle V1 discussed herein, no battery is part of thedrive train, and EM1 and EM2 operate in power balance.

To maintain power balance, the electromagnetic devices EM1 and EM2 maybe configured to operate in torque mode or voltage mode. Torque mode andvoltage mode may describe operational states of the electromagneticdevices. In torque mode, an electromagnetic device may be commanded tomaintain a given torque at the input of transmission T1. The torquecommand may depend on the speed of the electromagnetic device in torquemode and the electrical power requested to the wheels (as described inthe discussion of FIG. 16). In voltage mode, an electromagnetic devicemay be commanded to maintain a given voltage on the DC bus between EM1and EM2 (as described in the discussion of FIG. 15). Equivalently,voltage mode may describe the state of an electromagnetic deviceconfigured to perform whatever operations (i.e., motoring or generating)are required to maintain power balance with the other electromagneticdevice (in torque mode).

According to an exemplary embodiment, an electromagnetic device involtage mode may be motoring or generating—whichever is required tomaintain power balance with another electromagnetic device (in torquemode). For example, if EM1 and EM2 are in voltage mode and torque mode,respectively, and EM2 is motoring, then EM1 may be generating. EM1 maybe generating in order to provide the electrical power demanded by EM2as EM2 is motoring the vehicle. As another example, with EM1 and EM2 involtage mode and torque mode, respectively, EM1 may be motoring whileEM2 is generating. EM1 may be motoring in order to absorb and use theelectrical power EM2 is producing. EM1 may use the electrical power tomotor the vehicle.

Referring to FIG. 10, a flow diagram of a process 1000 for choosingvoltage mode and torque mode for electromagnetic devices EM1 and EM2 isshown, according to an exemplary embodiment. Process 1000 may choose theelectromagnetic device with higher power (higher speed or higher torqueor both) to be in voltage mode. Process 1000 may be carried out by acontrol system, such as control system 300 (FIG. 3) and/or a vehiclecontroller, such as vehicle controller 1902 (FIG. 19A). Though FIG. 10may refer to a specific electromagnetic device, e.g., EM1, as operatingin a particular mode, both EM1 and EM2 may be capable of operating asdescribed below.

Process 1000 includes operating electromagnetic device EM1 in voltagemode (1002). In voltage mode, EM1 may maintain the voltage on the DC busthat connects EM1 and EM2 as discussed in the description of FIG. 15.According to an exemplary embodiment, EM1 speed when the vehicle starts(i.e., when vehicle speed is zero) may be in the range of 1200 RPM to1800 RPM, depending on engine speed. According to some embodiments, EM1may be in voltage mode at low vehicle speeds (i.e., when thetransmission is output-coupled). In voltage mode, EM1 may be configuredto generate the electrical power demanded by EM2 in motoring thevehicle.

Process 1000 includes operating electromagnetic device EM2 in torquemode (1004), when EM1 is in voltage mode. According to some embodiments,EM2 may be in torque mode at low vehicle speeds. In torque mode, EM2 maymotor the vehicle, i.e., providing rotational mechanical energy to thetransmission of the vehicle to propel the vehicle.

Process 1000 includes determining whether electromagnetic device EM1will switch from voltage mode to torque mode (1006). EM1 may switchbetween voltage mode and torque mode depending on the speed of thedevice. According to some embodiments, EM1 may be required to maintain aminimum speed when in voltage mode. A minimum speed may be necessary sothat the voltage machine will generate enough electrical power tocontrol the DC bus voltage and supply the demand of the torque machine.When the speed of EM1 falls below a threshold (approximately 1200 RPM,according to some embodiments), EM1 may not be able may not be able togenerate sufficient power. At or near the threshold, EM1 may switch fromvoltage mode to torque mode, and EM2 may switch from torque mode tovoltage mode. When EM2 switches to voltage mode, its speed may be abovethe threshold. Thus, EM2 may generate sufficient electrical power tocontrol the DC bus voltage and supply EM1, which is now the torquemachine.

As described in the discussion of FIG. 10, EM1 speed may fall below athreshold because EM1 speed decreases as vehicle speed increases. EM2may have speed (in the negative direction) above the threshold when itswitches from torque mode to voltage mode. According to someembodiments, EM1 may switch from voltage mode to torque mode, and EM2may switch from torque mode to voltage mode when the vehicle istransitioning from low vehicle speeds to high vehicle speeds. EM1 mayswitch from torque mode to voltage mode, and EM2 may switch from voltagemode to torque mode when the vehicle is transitioning from high vehiclespeeds to low vehicle speeds.

Process 1000 includes changing the mode of electromagnetic device EM2(1008 and 1010), depending on the mode of electromagnetic device EM1.Electromagnetic device EM2 may switch modes in response to the mode ofelectromagnetic device EM2 to satisfy the condition that at least one(and only one) electromagnetic device is in voltage mode. Ifelectromagnetic device EM1 switches from voltage mode to torque mode,EM2 switches from torque mode to voltage mode (1008). If electromagneticdevice EM1 stays in voltage mode, then electromagnetic device EM2remains in torque mode (1010).

Because EM2 is operating in voltage mode at high vehicle speeds,coupling electromagnetic device EM2 to engine E1 (as EM2 is when thetransmission is input-coupled) may advantageously provide EM2 with astable speed. According to an exemplary embodiment, the transmission maybe switched to input-coupled mode before EM2 switches to voltage mode.This may advantageously allow for EM2 to stabilize with engine speed andprepare to operate in voltage mode.

Process 1000 describes choosing voltage mode and torque mode forelectromagnetic devices EM1 and EM2 when vehicle V1 is accelerating. Asimilar process may occur when vehicle V1 is decelerating. According toan exemplary embodiment, at high vehicle speeds, the transmission isinput-coupled, EM1 is the torque machine, and EM2 is the voltagemachine. EM1 speed may be high (in a negative direction). As vehiclespeed decreases, EM1 speed becomes more positive, passes through thezero speed point, and continues to increase. When EM1 speed is highenough in the positive direction (according to an exemplary embodiment,around 1200 RPM), EM1 may switch from torque mode to voltage mode, andEM2 may simultaneously switch from voltage mode to torque mode.Thereafter, the transmission may switch from input-coupled mode tooutput-coupled mode under the conditions described in FIGS. 6-8.

Electromagnetic devices EM1 and EM2 may be configured to switch betweentorque mode and voltage mode. Switching one electromagnetic device fromtorque mode to voltage mode and the other electromagnetic device fromvoltage mode to torque mode may advantageously manage the speeds of theelectromagnetic devices within acceptable ranges (described in thediscussion of FIG. 17, below). At a given time, EM1 may be in voltagemode and EM2 may be in torque mode. At a later time, EM1 may be intorque mode and EM2 may be in voltage mode. According to an exemplaryembodiment, at least one (and only one) electromagnetic device, may bein voltage mode at any given time (either EM1 or EM2, but not both).Operating only one electromagnetic device in voltage mode at a time mayadvantageously avoid stacking control loops (such as process 1500 ofFIG. 15) and making the DC bus unstable. At least one electromagneticdevice may be in voltage mode at any time because no other energy source(e.g., a battery) is present to provide electrical energy demanded bythe other electromagnetic device.

Electromagnetic devices EM1 and EM2 may be configured to switch modessimultaneously. According to an exemplary embodiment, controller areanetwork (CAN) messaging may be implemented to allow simultaneousswitching. A single CAN message may be sent to EM1 and EM2 to assignvoltage mode and torque mode. Switching modes simultaneously mayadvantageously avoid both machines being in voltage mode at the sametime. A simultaneous switch may also advantageously avoid any suddentorque changes by one or both of the electromagnetic devices.

Referring to FIG. 11, a chart 1100 of operational modes ofelectromagnetic devices EM1, EM2 is shown, according to an exemplaryembodiment. Chart 1100 includes periods when vehicle V1 is inoutput-coupled mode (1102), switching between output-coupled mode andinput-coupled mode (1104), and in input-coupled mode (1106). Accordingto an exemplary embodiment, vehicle V1 may be in output-coupled mode atlow vehicle speeds and in input-coupled mode when vehicle V1 at highvehicle speeds.

Chart 1100 shows that engine E1 is in speed mode for all vehicle speeds.As described in the discussion of FIG. 5, engine E1 is coupled to thering gear G1 of planetary gear set P1. The output of planetary gear setP1 is coupled to planetary gear carrier PGC1. Thus, the engine isdecoupled from the output of the transmission for all vehicle speeds.This may enable engine E1 to be advantageously commanded at a particularspeed (and not a particular torque) for all vehicle speeds. The processfor choosing engine speed is described in the discussion of FIG. 14.According to an exemplary embodiment, an optimum and/or fuel-efficientspeed is chosen for engine speed.

Chart 1100 shows that that electromagnetic device EM1 is in voltage modeand electromagnetic device EM2 is in torque mode when vehicle V1 isoutput-coupled (1102). In torque mode, EM2 may be motoring the vehicleto propel the vehicle. In voltage mode, EM1 may be generating to supplythe electrical energy demanded by EM2. In output-coupled mode, EM1 iscoupled to sun gear G3 of planetary gear set P1 (FIGS. 2, 5). EM2 iscoupled to the planetary gear carrier (output) of planetary gear set P1(FIGS. 2, 5). Because EM2 is coupled to the output of planetary gear setP1, EM2 torque is being used to propel the vehicle, and EM2 speedincreases as vehicle speed increases. Thus, the power (from EM2) beingused to propel the vehicle may increase as vehicle speed increases.Because EM1 is coupled to the sun gear G1, EM1 speed decreases asvehicle speed increases. Thus, the power being generated by EM1 maydecrease as vehicle speed increases. EM1 may switch to torque mode whenthe power being generated is too low to supply EM2 (as described indiscussion of FIG. 10).

Chart 1100 shows that that EM1 is in voltage mode and EM2 is in torquemode when vehicle V1 is transitioning between output-coupled mode andinput-coupled mode (1104). EM2 may be motoring in torque mode, and EM1may be generating in voltage mode. According to an exemplary embodiment,vehicle V1 may switch from output-coupled mode to input-coupled modebefore EM1 and EM2 switch between voltage mode and torque mode. Theoutput-coupled/input-coupled transition may occur when EM2 speed reachesan upper limit (as discussed in FIG. 6). The voltage/torque transitionmay occur when EM1 speed reaches a lower limit (as discussed in FIG.10). Completing the output-coupled/input-coupled transition before thevoltage/torque transition may advantageously allow for EM2 to stabilizewith a more steady engine speed before EM2 becomes the voltage machine.

Chart 1100 shows that EM1 is in torque mode and EM2 is in voltage modewhen vehicle V1 is in input-coupled mode (1104). EM1 may be motoring intorque mode, and EM2 may be generating in voltage mode. In input-coupledmode, EM2 is coupled to engine E1. EM1 is coupled to engine E1 and theoutput of the planetary gear set P1. Because it is coupled to the outputof the planetary gear set P1, EM1 speed increases (in the negativedirection), as vehicle speed increases. EM1 speed may be reduced as EM1speed reaches an upper limit. EM2 speed stays relatively steady becauseengine speed stays relatively steady. According to an exemplaryembodiment, engine speed is maintained at an optimum and/orfuel-efficient speed, for all vehicle speeds. Engine speed may beincreased or decreased depending on the power required (e.g., more powerrequired to accelerate) and on speed constraints (e.g., upper limits) onEM1 and EM2. Selection of engine speed is described in the discussion ofFIG. 14, below.

In some embodiments, EM1 speed and EM2 speed may be fixed when thevehicle speed and engine speed are controlled. Vehicle speed may becontrolled by an operator the vehicle by providing inputs (via, e.g., anaccelerator pedal) that cause the vehicle to accelerate and decelerate.Engine speed may be controlled at an optimum and/or fuel-efficientspeed. EM1 speed is coupled to the engine speed and wheel speed via theplanetary gear set because EM1 is coupled to the sun gear. EM1 speed mayfixed when the engine speed and wheel speed are determined as a resultof the kinematic constraints of the planetary gear set. When thetransmission is output-coupled, EM2 speed is coupled to the wheel speedvia the planetary gear set. (EM2 and output are coupled to the planetarygear carrier in output-coupled mode.) As a result EM2 speed isproportional to wheel speed. When the transmission is input-coupled, EM2speed is coupled to the engine speed via the planetary gear set. (EM2and engine are coupled to the ring gear in input-coupled mode). As aresult, EM2 speed is proportional to the engine speed.

Referring to FIG. 12, a chart 1200 for determining whetherelectromagnetic devices EM1, EM2 are motoring or generating is shown,according to an exemplary embodiment. The operations represented inchart 1200 may be carried out by a control system, such as controlsystem 300 (FIG. 3) and/or vehicle controller, such as vehiclecontroller 1902 (FIG. 19A). Though FIG. 12 may refer to a specificelectromagnetic device, e.g., EM2, as motoring or generating, both EM1and EM2 may be capable of operating as described below.

Chart 1200 includes whether the transmission is output-coupled orinput-coupled (1202). According to an exemplary embodiment, the vehiclespeeds may be low when the transmission is output-coupled and high whenthe transmission is input-coupled. Chart 1200 also includes theoperating state of the electromagnetic device in torque mode (1204) andin voltage mode (1206). As described in the discussion of FIG. 11, EM1may be in voltage mode and EM2 may be in torque mode when transmissionT1 is output-coupled. EM1 may be in torque mode and EM2 may be involtage mode when transmission T1 is input-coupled. According to anexemplary embodiment, electromagnetic devices EM1, EM2 may be motoringor generating. Chart 1200 also includes the conditions under which thevoltage machine and torque machine operate as indicated (1208).

In motoring mode, an electromagnetic device may apply torque at itsoutput in the same direction as its speed and may power the transmissionof the vehicle to propel the vehicle. In generating mode, anelectromagnetic device may apply torque at its output in the oppositedirection as its speed and may generate power as required by the otherelectromagnetic device. Positive and negative are used indicate relative(and not absolute) directions of torque and speed. For example, the EM1speed and torque are in the same direction when both are positive orboth are negative. EM1 speed and torque are in opposite direction whenone is positive and one is negative.

EM1 and EM2 may be configured to switch between motoring and generating.EM1 and EM2 may be further configured to motor and generate while involtage mode and torque mode. Whether the electromagnetic devices EM1and EM2 are motoring or generating may depend on whether they are intorque mode or voltage mode, and whether transmission T1 isoutput-coupled or input-coupled.

Chart 1200 shows that when the vehicle is accelerating in output-coupledmode, EM2 is motoring and EM1 is generating (1210). Because EM2 ismotoring in torque mode, EM1, in voltage mode, may be generating tosupply EM1's power demand. When EM2 is motoring, EM2 torque is in thesame direction as EM2 speed. According to an exemplary embodiment, bothEM2 torque and speed may be in the negative direction. When EM1 isgenerating, EM1 torque is in the opposite direction as EM1 speed.According to an exemplary embodiment EM1 torque may be negative and EM1speed may be positive.

Chart 1200 shows that when the vehicle is applying torque in thedirection opposite its speed in output-coupled mode, EM2 is generating,and EM1 may be motoring or generating. That is, the vehicle may beapplying a braking torque. This situation may arise, e.g., when avehicle is rolling backwards on uphill terrain. A vehicle operator maybe attempting to motor the vehicle uphill. In output-coupled mode, EM2is coupled to the transmission output. EM2 is providing a forward torquefor the vehicle to move uphill. Because the vehicle is moving backwards,the speed is opposite the torque, and EM2 is generating.

When EM2 is generating in output-coupled mode, EM1 may be motoring orgenerating depending on whether the power generated by EM2 is greaterthan the overall power loss on the DC bus (1016). When the powergenerated by EM2 is greater than the overall power loss, EM1, in voltagemode, may be motoring. By motoring, EM1 may maintain the voltage rangeon the DC bus by using the power generated by EM1. When EM1 is motoring,the torque and speed of EM1 are in the same direction. When the overallpower loss on the DC bus is greater than the power generated by EM2,EM1, in voltage mode, may be generating. By generating, EM1 may maintainthe voltage range on the DC bus by supplementing the power generated byEM2. When EM1 is generating, the torque and speed of EM1 are in theopposite direction.

Chart 1200 shows that EM1, in torque mode, may be motoring (1214) orgenerating (1216) when the transmission is input-coupled. According toan exemplary embodiment, EM1 may switch from generating to motoring asvehicle speed increases. As described in the discussion of FIGS. 2 and5, EM1 is coupled to the sun gear of the planetary gear set. As vehiclespeed increases, EM1 speed decreases (i.e., becomes more negative).According to an exemplary embodiment, EM1 speed may be positive when thetransmission switches from output-coupled to input-coupled mode. EM1speed may decrease as vehicle speed increases, cross the zero speedpoint, and continue decreasing (i.e., becoming more negative). Accordingto an exemplary embodiment, EM1 torque may be negative for all vehiclespeeds. Thus, EM1 may switch from generating to motoring mode when EM1speed crosses the zero speed point, from positive speed (generating) tonegative speed (motoring).

EM1 is motoring (1214) when EM1 torque is in the same direction as EM1speed. According to an exemplary embodiment, both EM1 torque and speedmay be negative. When EM1 is motoring, power is flowing from the sungear to the wheels of the vehicle. If EM1 is motoring in torque mode,EM2 may be generating in voltage mode. When EM2 is generating, EM2torque and EM2 speed are in opposite directions. According to anexemplary embodiment, EM2 torque may be positive while EM2 speed isnegative.

EM1 is generating (1216) when EM1 torque is in the opposite direction asEM1 speed. According to an exemplary embodiment, EM1 torque may benegative (as it may be for all vehicle speeds), and EM1 speed may bepositive. When EM1 is generating, power is flowing to the sun gear fromthe engine. When EM1 is generating in torque mode, EM2 may be motoringor generating in voltage mode. EM2 may be motoring or generatingdepending on whether the power generated by EM1 is greater than theoverall power loss on the DC bus. When the power generated by EM1 isgreater than the overall power loss, EM2, in voltage mode, may bemotoring. By motoring, EM2 may maintain the voltage range on the DC busby using the power generated by EM1. When EM2 is motoring, the torqueand speed of EM2 are in the same direction. When the overall power losson the DC bus is greater than the power generated by EM1, EM2, involtage mode, may be generating. As described in the discussion of FIG.9C, this situation may arise when both EM1 and EM2 are at or near zeropower (i.e., torque×speed=0). By generating, EM2 may maintain thevoltage range on the DC bus by supplementing the power generated by EM1.When EM2 is generating, EM2 torque and speed are in opposite directions.According to an exemplary embodiment, EM2 torque may be positive and EM2speed may be negative.

Power Device Commands

In the drive train of vehicle V1, power may flow from engine E1, toplanetary gear set P1, and then to the wheels of vehicle V1 (i.e., thetransmission drives one or more axles configured to provide rotationalenergy to the wheels to propel vehicle V1). According to an exemplaryembodiment, mechanical power from engine E1 may be diverted into twopaths: electrical and mechanical. From engine E1, mechanical power maytake a path to ring gear G1 (coupled to engine E1), to planetary gearcarrier PGC1 (coupled to the output of planetary gear set P1), and thento the wheels. From engine E1, electrical power (i.e., power that flowsthrough electromagnetic devices EM1, EM2) may take a path to ring gearG1, to sun gear G1, to planetary gear carrier PGC1, and then to thewheels. In the electrical path, mechanical power from the engine appliesa mechanical torque at the input of the generating electromagneticdevice. The generator coverts the mechanical torque to electrical power.The motor converts the electrical power to a mechanical torque, which isapplied to the planetary gear set and outputted to motor the vehicle.

In some embodiments, engine E1 may be the primary source of power.According to an exemplary embodiment, engine E1 may be operatedparticular speeds (and not particular torques) for all vehicle speeds.As described in the discussion of FIGS. 2 and 5, engine E1 is coupled toring gear G1 of planetary gear set P1 for all vehicle speeds, while theoutput of planetary gear set P1 is coupled to the planetary gear carrierPGC1. This configuration may advantageously decouple engine speed fromvehicle speed for all vehicle speeds. This may also may advantageouslyallow for selection of an engine speed that optimizes fuel economy.

At any given time, the power that is available to be delivered to thewheels of vehicle V1 may depend on the status of the system. The systemstatus may be determined by the vehicle speed, engine speed, enginepower available, coupling ratios, transmission ratios, etc. The powerand torque that is delivered to the wheels may depend on the demand(i.e., throttle input). For example, with 50% throttle input, 50% of theavailable power may be delivered to the wheels. The available powerdemanded determines how much torque must be applied to theelectromagnetic device in torque mode. The other electromagnetic device,in voltage mode, generates power that is available to the torquemachine.

Referring to FIG. 13, a plot of simulated output power available asfunction of engine speed is shown, according to an exemplary embodiment.The x-axis of the plot shows engine speed. The y-axis of the plot showsmaximum output power available to be delivered to the wheels to drivethe vehicle. According to an exemplary embodiment, the wheels of thevehicle may receive power from the output of the planetary gear carrierand EM2, depending upon transmission configuration. For example, inoutput-coupled mode, both the planetary gear carrier and EM2 are coupledto the axle driving the wheels, so both the planetary gear carrier andEM2 may apply torque to wheels. In some embodiments, power available mayvary with vehicle speed. FIG. 13 may be considered an instantaneousrepresentation of the power available at vehicle speed of approximately16 mph.

According to an exemplary embodiment, engine power may not include powerrequired to sustain accessory loads. An accessory load may be, e.g., asteering pump. Engine power may be utilized in order to operate theaccessory. As a result, that engine power is not available to bedelivered to the wheels of the vehicle. Powerflow controller 1904 (FIG.19A) may be configured to compute the number and load of accessorydevices, and determine the engine power available to output lessaccessory loads.

FIG. 13 shows the output power of the engine as engine speed increases.The engine power curve is indicated with squares. The engine power shownmay represent the power that would be available to the wheels of thevehicle (except for losses) were the engine directly coupled thetransmission, as in a conventional vehicle that does not utilizeelectromagnetic devices as part of its drive train. In some embodiments,power available may vary with the configuration of the transmission.FIG. 13 shows output-coupled power curve, which is indicated withcircles, and the input-coupled power curve, which is indicated withtriangles. The output-coupled and input-coupled power curves mayrepresent the power that is available to be delivered to the wheels ofthe vehicle when the transmission is so configured. The transmission maybe configured to switch between input-coupled and output-coupled mode atany engine speed. The configuration may be advantageously chosen at agiven vehicle speed and engine speed so that, e.g., more power isavailable to drive the vehicle. The power available may be computed aspart of calculating optimum engine speed (process 1400 of FIG. 14) andcalculating the torque command for the torque machine (process 1600 ofFIG. 16). Power available may be computed by powerflow controller 1904(FIG. 19A).

FIG. 13 shows the output power of the engine (1302) for varying enginespeeds. The total available power to be delivered to the wheels dependson the engine speed. As shown on the left side of the plot, poweravailable increases as engine speed increases. According to an exemplaryembodiment, both output-coupled power 1304 and input-coupled power 1306track the maximum engine power available for low engine speeds.

In some embodiments, not all of the power that is available at a givenengine speed may be outputted, due to varying transmissionconfigurations. The transmission may not deliver all of the poweravailable to the wheels in order to satisfy other constraints on thedrive train. The constraints may include, e.g., maintainingelectromagnetic devices EM1, EM2 within acceptable operating speeds.According to an exemplary embodiment, a portion of total power (i.e.,power that the engine can support) delivered the output flows in theelectrical path. In some embodiments, the portion of power in theelectrical path is fixed. In some embodiments, the portion of power inthe electrical path depends on the transmission configuration (i.e.,input-coupled or output-coupled) and the ratio of wheel speed to enginespeed (i.e., the ratio of electrical power to total power). In someembodiments, the portion of power in the electrical path varies based onthe gear ratios of the transmission. The portion of power in theelectrical path is determined by the speed and torque of theelectromagnetic devices EM1, EM2. As described in the discussion of FIG.12, EM1 speed may be determined by wheel speed and engine speed viakinematic speed constraints of the planetary gear system that theengine, EM1, and the wheels are kinematically attached to. EM2 speed iscoupled to wheel speed in output-coupled mode and is coupled to enginespeed in input-coupled mode. Therefore, as the wheel speed (or vehiclespeed) changes, the speeds of EM1 and EM2 change. For a given vehiclespeed, the power deliverable to the wheels depends on the power that canbe supported by the engine and the requirement that a portion of thepower flow in the electrical path. If the required portion of power inthe electrical path is not available (because of the speeds and/ortorques of EM1, EM2), then total power supported by the engine cannot bedelivered to the wheels. As a result, the available power curve deviates(downwards) from engine power curve, as shown in input-coupled powercurve and output-coupled power curve of FIG. 13.

At a given engine speed, input-coupled power 1306 may be greater thanoutput-coupled power 1304, or output-coupled power 1304 may be greaterthan input-coupled power 1306. As shown near the middle of FIG. 13,output-coupled power 1304 equals maximum engine power available for agreater portion of engine speeds than input-coupled power. Thus, asdescribed in the discussion of FIGS. 7 and 8, the transmission mayadvantageously remain output-coupled longer in order to provide thevehicle with more power.

Referring to FIG. 14, a process 1400 for calculating engine speed isshown, according to an exemplary embodiment. Process 1400 may be carriedout by a control system, such as control system 300 (FIG. 3) and/orvehicle controller, such as vehicle controller 1902 (FIG. 19A). Inparticular, engine speed may be computed by engine control module 1910of powerflow controller 1904. According to an exemplary embodiment,engine control module 1910 may receive input from vehicle status module1922 regarding vehicle data (e.g., current vehicle speed). Enginecontrol module 1910 may also transmit engine control data (e.g.,selected optimum engine speed), to engine 1952 of the vehicle. Enginecontrol module 1910 may also receive data from and transmit data toother modules of powerflow controller 1902.

Process 1400 includes measuring current vehicle speed (1402). Vehiclespeed may be measured by, e.g., a wheel speed sensor. Once measured,vehicle speed may be transmitted to and received by powerflow controller1904 (FIG. 19A). For example, vehicle status module 1922 may receivevehicle speed and transmit the data to engine control module 1910.

Process 1400 includes determining throttle fractional input. In someembodiments, throttle fractional input may be measured by an acceleratorinput sensor. An accelerator input sensor may measure the position ofthe accelerator pedal. This, in turn, may determine the amount of powerrequested to the wheels of the vehicle. For example, a vehicle operatormay request no power when the accelerator pedal is not depressed. Theaccelerator input may be transmitted to powerflow controller 1904 (FIG.19A). Powerflow controller 1904 may calculate the throttle fractionalinput.

Process 1400 includes computing maximum power deliverable at currentvehicle speed (1406). Maximum power deliverable may depend currentvehicle speed and current engine speed, as depicted in the plot of FIG.13. Maximum power deliverable may be computed by power calculationmodule 1920 of powerflow controller 1904.

Process 1400 includes computing throttle proportional power (1408).Throttle proportional power may be calculated by multiplying the maximumpower deliverable at current vehicle speed to the throttle fractionalinput. Throttle proportional power describes the power requested to thewheels greater than or less than the power currently being delivered tothe wheels. Throttle proportional power may be computed by powerflowcontroller 1904 (FIG. 19A).

Process 1400 includes determining the engine speed range that canprovide the throttle proportional power (1410). The engine speed rangemay be a maximum speed and a minimum speed between which the requiredthrottle proportional power can be provided. If the requested throttleproportional power is higher than the current throttle proportionalpower (i.e., the vehicle is accelerating), the current engine speed maybe increased, if increasing engine speed will increase powerdeliverable. The engine speeds vs. power available data shown in FIG. 13may be utilized to determine an acceptable engine speed range. With theacceptable engine speed, the electromagnetic device coupled to theengine may be able to generate sufficient power for the otherelectromagnetic device to motor the wheels at the desired vehicle speed.Engine speed range may be computed by engine control module 1910 ofpowerflow controller 1904 (FIG. 19A).

Process 1400 includes selecting and commanding the optimum speed fromthe identified range (1412). In some circumstances, the optimum speedmay the lowest speed in the identified range. The lowest speed may bethe most fuel-efficient speed. In other circumstances, the optimum speedmay be one of the other speeds in the identified range. For example, ininput-coupled mode, EM1 may approach a maximum speed in the negativedirection. Because of how EM1 is coupled to engine E1, increasing enginespeed may make EM1 speed more positive (less negative). Thus, an optimumengine speed that is higher than the minimum speed in the range may bechosen to advantageously maintain EM1 speed within acceptable limits.

The engine speed may be determined by engine control module 1910 ofpowerflow controller 1904 (FIG. 19A). The engine speed choice may dependon a variety of vehicle conditions, e.g., speed constraints onelectromagnetic devices EM1, EM2. Vehicle conditions may be received atengine control module 1910 from other components of powerflow controller1904. Speed constraints on EM1 and EM2 may be received from, e.g., powercalculation module 1920. For example, the chosen engine speed may behigher than the lowest speed in the identified range if the speed of oneof the electromagnetic devices EM1, EM2 is too high or too low.

According to an exemplary embodiment, engine speed may be selected sothat, in combination with the vehicle speed, electrical power losses areadvantageously minimized. In some embodiments, the electrical power paththrough transmission T1 may be less efficient than the mechanical powerpath. As a result, more power may be lost if there is a more power inthe electrical path. The ratio of electrical power to total power is afunction of the transmission ratio. Thus, the flow of electrical powermay govern the flow of total power from the input to the output of thetransmission. As described in FIGS. 2 and 5, EM1 is coupled to the sungear G3 of planetary gear set P1. EM1 speed may determine the proportionof electrical power in the system. According to an exemplary embodiment,a higher EM1 speed may correspond to a greater percentage of power inthe electrical path. An engine speed may be selected, that incombination with the vehicle speed, minimizes EM1 speed and electricalpower losses.

According to an exemplary embodiment, an electromagnetic device involtage mode may be operated using closed loop control on the voltage ofthe DC bus between electromagnetic devices EM1, EM2. The closed loopcontrol may direct the electromagnetic device in voltage mode tomaintain a voltage between a specified range. When the voltage isoutside of the range, the voltage machine may act as required (i.e.,generate more, generate less, consume more, or consume less) to put thevoltage back into range. The closed loop control may be implemented by acontrol system, such as control system 300 (FIG. 3), or by EM1 commandmodule 1912 or EM2 command module (FIG. 19A). In other embodiments,different control structures may be implemented.

Referring to FIG. 15, a process 1500 for operating a voltage machineusing closed loop control is shown, according to an exemplaryembodiment. Process 1500 includes setting an upper and lower thresholdfor the voltage on the DC bus between electromagnetic devices EM1 andEM2 (1502). In some embodiments, the upper and lower thresholds may beset by, e.g., a manufacturer of the vehicle, etc. In some embodiments,the upper and lower thresholds may be configurable by an operator of thevehicle. In some embodiments, a fixed voltage (and not a range ofvoltages) is commanded to the voltage machine. In other embodiments, thevoltage machine may be configured to a maintain a mean value of aspecified voltage range. In still other embodiments, the voltage orvoltage range may be fluctuating or dynamically changing based on thestatus of the vehicle.

Process 1500 includes measuring the line voltage on the DC bus (1504).The voltage may be measured at different intervals. In some embodiments,voltage may be measured based on time (e.g., every two milliseconds). Inother embodiments, voltage may be measured based on changes to theoperating status of the vehicle and/or its components (e.g., whenever anelectromagnetic device changes speed or torque by 1%, etc.). The linevoltage may be measured by a sensor of one or both electromagneticdevices EM1, EM2. The sensor may transmit data to powerflow controller1904 (FIG. 19A). The DC bus may also be configured to transmit voltagefeedback to powerflow controller 1904 (FIG. 19A).

Process 1500 includes determining if the line voltage is less than thelower threshold (1506). If so, the voltage machine may be commanded toincrease the DC bus voltage to above the lower threshold. The voltagemachine's action may depend whether the voltage machine is motoring orgenerating. Thus, process 1500 includes determining if the voltagemachine is motoring or generating (1508). If the voltage machine ismotoring, then the voltage machine may decrease torque (1510). Bydecreasing its torque, the voltage machine may require less electricalpower, leading to a net increase of the DC bus voltage (because thetorque machine may be generating without changing torque). If thevoltage machine is generating, then the voltage machine may increasetorque (1512). By increasing its torque, the voltage machine maygenerate more electrical power, leading to a net increase of the DC busvoltage (because the torque machine may be motoring without changingtorque). If the voltage machine decreases torque (1510) or increasestorque (1512), the control loop may continue (1522), and the DC busvoltage may be measured again at the next interval.

When the DC bus voltage is not less than the lower threshold, process1500 includes determining if the line voltage is greater than the upperthreshold (1514). If so, the voltage machine may be commanded todecrease the DC bus voltage to below the upper threshold. As it was whenthe line voltage was less than the lower threshold, the action requiredmay depend on whether the voltage machine is motoring or generating.Thus, process 1500 include determining if the voltage machine ismotoring or generating (1516). If the voltage machine is motoring, thenthe voltage machine may increase torque (1518). By increasing itstorque, the voltage machine may consume more electrical power, leadingto a net decrease of the DC bus voltage (because the torque machine maybe generating without changing torque). If the voltage machine isgenerating, then the voltage machine may decrease torque (1520). Bydecreasing its torque, the voltage machine may generate less electricalpower, leading to a net decrease of the DC bus voltage (because thetorque machine may be motoring without changing torque). If the voltagemachine increases torque (1518) or decreases torque (1520), the controlloop may continue (1522), and DC bus voltage may be measured again(1504) at the next interval.

Process 1500 includes continuing the DC bus control loop (1522) when theline voltage is between the upper and lower thresholds, and when thevoltage machine has increased or decreased its torque to adjust to theline voltage to within range. When the DC bus control loop continues,the line voltage is measured again (1504) at the next interval. In someembodiments, the voltage machine may increase or decrease speed, asrequired, instead of or in addition to changing torque.

Referring to FIG. 16, a process 1600 for determining the torque commandfor the electromagnetic device in torque mode is shown, according to anexemplary embodiment. Process 1600 may be carried out by a controlsystem, such as control system 300 (FIG. 3) and/or vehicle controller,such as vehicle controller 1902 (FIG. 19A). According to an exemplaryembodiment, EM1 command module 1912 or EM2 command module 1914 maycompute the torque command and transmit it to EM1 1954 or EM2 1956.

Process 1600 includes measuring current speeds of the vehicle, engine,EM1, and EM2 (1602). As described in the discussion of FIG. 14, vehiclespeed may be measured by a vehicle speed sensor and transmitted tovehicle status module 1922 of powerflow controller 1904 (FIG. 19A).Engine speed may be measured and monitored by engine control module1910. EM1 and EM2 speeds may be measured and monitored by EM1 commandmodule 1912 and EM2 command module 1914. Vehicle status module 1922,engine control module 1910, EM1 command module 1912, and EM2 commandmodule 1914 may transmit the respective speeds to the command module ofthe electromagnetic device in torque mode.

Process 1600 includes measuring throttle fractional input (1604),calculating maximum power deliverable (1606), and calculating throttleproportional power (1608). These steps may be completed substantially asdescribed in process 1400 (FIG. 14). According to an exemplaryembodiment, throttle fractional input may be computed by vehicle statusmodule 1922, and maximum power deliverable and throttle proportionalpower may be computed by power calculation module 1920. The calculationsmay be transmitted to the command module of the electromagnetic devicein torque mode.

Process 1600 includes calculating an electric power proportion (EPP)number (1610). The electric power proportion number may be calculatedbased on the engine speed and vehicle speed. In some embodiments, theEPP is a ratio of electrical power to total (i.e., electrical andmechanical) power in the system. According to an exemplary embodiment,the ratio of electrical power to total power is equal to a function ofcurrent engine speed (measured in step 1602) to current vehicle speed(measured in step 1602). The electrical to total power ratio may changewhen the engine speed or vehicle speed changes. The electrical power(i.e., the power from electromagnetic devices EM1, EM2) in planetarygear set may flow through the sun gear. (EM1 is coupled to the sun gear,as described in FIGS. 2 and 5). The ratio of power flowing through thesun gear to the total power flowing to the wheels of the vehicle (fromthe output of the planetary gear set and, in input-coupled mode, fromEM2) is equal to a function of engine speed and vehicle speed. This isthe result of constraints on the torques and speeds of the planetarygear set arising from gear teeth ratios. The power in the planetary gearset may be constrained when the torques and speeds are constrained. Thepower ratio (e.g., engine power input to planetary gear set poweroutput, or, equivalently, power into the ring gear to power out of thecarrier gear) is also constrained. The power ratio may change when theengine speed or vehicle speed changes. The ratio of electrical power tototal power may vary depending on if the transmission is input-coupledor output-coupled. The ratios may differ for input-coupled mode andoutput-coupled mode, but the ratio of electrical power to total power isstill a function of the engine speed and vehicle speed for bothtransmission modes.

According to an exemplary embodiment, a small electric power proportionnumber may be maintained to achieve efficiency. As described in thediscussion of FIG. 14, more electrical power in the system may present apossibility of higher losses because the electrical power path is lessefficient than the mechanical power path. According to an exemplaryembodiment, power calculation module 1920 may compute the electric powerproportion number.

Process 1600 includes calculating the required electrical power (1612).The required electrical power may be calculated based on the electricpower proportion number (calculated in step 1604) and the throttleproportional power (calculated in step 1208). According to an exemplaryembodiment, the required electrical power is calculated by multiplyingthe electric power proportion number and the throttle proportionalpower. The throttle proportional power is the total power requested by avehicle operator. The required electrical power is the portion of thetotal power that will flow through electromagnetic devices EM1, EM2.

Process 1600 includes determining and commanding a torque to the torquemachine (1614). The torque command may be determined by considering therequired electrical power (calculated in step 1606) and the speed of thetorque machine (measured in step 1602). The torque command may becomputed by dividing the required electrical power by the speed. Thespeed of the torque machine may depend on the speed of engine E1. Forexample, in input-coupled mode, both EM1 and EM2 are coupled to engineE1. When the required electrical power is high, the commanded torque mayalso be high. According to an exemplary embodiment, the command moduleof the electromagnetic device in torque mode may compute the torquecommand. Powerflow controller 1904 may utilize a power loss estimationmodel to improve the torque command. A power loss estimation model maybe a regression analysis completed on experimental data that allowspowerflow controller 1904 to predict what the electrical power loss willbe at a particular speed and torque. Using the model, the torque commandcan be adjusted to compensate for losses.

Referring to FIG. 17, a chart of speed constraints for the engine, theelectromagnetic device in voltage mode, and the electromagnetic devicein torque mode is shown, according to an exemplary embodiment. The chartof FIG. 17 shows the speed range of the engine is between an identifiedrange (1702). The range of may be calculated in process 1400 (FIG. 14).The range at given time may represent the engine speeds that can deliverthe throttle proportional power requested at that time. The engine speedrange may be calculated by engine control module 1910, and a chosenengine speed may be transmitted to engine 1952 (FIG. 19A).

The chart of FIG. 17 shows the speed range of the electromagnetic devicein voltage mode is above a minimum speed and below a maximum speed(1704). Electromagnetic devices EM1, EM2 may both be operated in torquemode or voltage mode. As described in FIG. 10, the electromagneticdevice in voltage mode may be maintained above a minimum speed so thatit may generate sufficient power to supply the power demand of thetorque machine. According to an exemplary embodiment, a minimum speedmay be 1200 RPM. The voltage machine may be maintained below a maximumspeed in order to avoid a mechanical fault. The maximum speed may dependon the particular electromagnetic device being used and may be set by amanufacturer of the device. According to an exemplary embodiment, amaximum speed may be 6000 RPM.

The chart of FIG. 17 shows the speed range of the electromagnetic devicein torque mode is below a maximum speed (1704). Like the voltagemachine, the torque machine may be maintained below a maximum speed inorder to avoid a mechanical fault. The maximum speed may depend on theparticular electromagnetic device being used and may be set by amanufacturer of the device. According to an exemplary embodiment, amaximum speed may be 6000 RPM. In some embodiments, the torque machinemay not have a minimum speed because the torque machine is notresponsible for generating power to be used by another electromagneticdevice.

Referring to FIGS. 18A-18D, plots of simulated operation of vehicle V1are shown, according to exemplary embodiments. The plots of 18A-18Ddescribe one embodiment of the general relationship of the quantitiescontained therein. The specific values reflected on the plots of FIGS.18A-18D may be different in different embodiments. In some embodiments,the data depicted in FIGS. 18A-18D may be stored in memory of powerflowcontroller 1904 of FIG. 19A. The data may be retrieved by an operator ofthe vehicle, and a history of the plots shown in FIGS. 18A-18D may becreated. In the embodiments of FIGS. 18A-18D, the vehicle is operated atfull throttle beginning at t=10 sec.

Referring to FIG. 18A, a plot of simulated vehicle speed as a functionof time is shown, according to an exemplary embodiment. The plot of FIG.18A shows that vehicle speed steadily increases, as expected, when thevehicle is operated at full throttle.

Referring to FIG. 18B, a plot of simulated engine speed and speeds ofelectromagnetic devices EM1, EM2 is shown, according to an exemplaryembodiment. Engine speed is shown to be relatively constant for allvehicle speeds. This is expected from the coupling of the engine. Asdescribed in FIGS. 2 and 5, the engine is coupled to the ring gear G1 ofplanetary gear set P1. The engine is decoupled from the output ofplanetary gear set P1. Thus, as shown in FIG. 18B, engine speed isdecoupled from vehicle speed for all vehicle speeds. According to anexemplary embodiment, the engine may be commanded at an optimum and/orfuel-efficient speed. As described in the discussion of FIG. 14, enginespeed may be chosen to maintain electromagnetic devices withinacceptable operating speeds. As discussed below, this is shownapproximately between t=11 sec and t=15 sec.

EM2 speed is shown to increase rapidly in magnitude when the vehiclespeed begins to increase. This is expected from the coupling of EM2 inoutput-coupled mode. As described in FIGS. 2 and 5, EM2 is coupled tothe output of the planetary gear set P1 with a high gear ratio. When theEM2 speed reaches a threshold beyond which it cannot operate, thetransmission switches configuration from output-coupled mode toinput-coupled mode. In input-coupled mode, EM2 is coupled to the engine,which has a lower and more steady speed. As reflected in FIG. 18B, EM2speed is shown to decrease and become more steady. According to anexemplary embodiment, EM2 may switch from torque mode to voltage modeafter the transmission becomes input-coupled. As described in thediscussion of FIG. 11, a more steady EM2 speed may be advantageous whenEM2 is the voltage machine.

EM1 speed is shown to decrease (i.e., become more negative) as vehiclespeed increases. This is expected from the coupling of EM1. As describedin FIGS. 2 and 5, EM1 is coupled to the sun gear G3 of planetary gearset P1 for all vehicle speeds. As described in the discussion of FIG.10, EM1 may switch from voltage mode to torque mode because EM1 speedsare too low to maintain a voltage on the DC bus. EM1 speed continues tobecome more negative as vehicle speed increases. Early in theacceleration of the vehicle (approximately between t=11 sec and t=15sec), engine speed is increased in order to maintain a relativelyconstant EM1 speed. As described in FIGS. 2 and 5, EM1 speed increasesas engine speed increases. Engine speed may be increased to counteractdecreasing EM1 speeds at increasing vehicle speeds.

Referring to FIG. 18C, a plot of simulated engine torque and torques ofthe electromagnetic devices EM1, EM2 is shown, according to an exemplaryembodiment. According to an exemplary embodiment, EM1 and EM2 torque maybe increased or decreased in order to generate or motor with the powerrequired for power balance. This is described in the discussion of FIG.15.

Referring to FIG. 18D, a plot of simulated power of the electromagneticdevices EM1, EM2 is shown, according to an exemplary embodiment. EM1power is shown to be approximately a mirror image of EM2 power acrossthe zero power line. This is expected because EM1 and EM2 operate inpower balance. As described in “Power Balance,” above, at any givenvehicle speed, one of the electromagnetic devices is providing theelectrical power required (and only the electrical power required) bythe other electromagnetic device. The sum of EM1 power and EM2 power maybe approximately zero for all vehicle speeds. (Because of power losses,the sum may be not be exactly zero.) According to an exemplaryembodiment, an electromagnetic device is motoring when its power ispositive (i.e., its speed and torque are in the same direction). Anelectromagnetic device is generating when its power is negative (i.e.,its speed and torque are in opposite directions).

Control Electronics

Referring to FIG. 19A, a block diagram of a vehicle controller 1902 isshown, according to an exemplary embodiment. Vehicle controller 1902 is,generally, hardware and/or software configured to control, monitor, andmanage systems in a vehicle. Vehicle controller 1902 may be composed ofone or more electronic control units (e.g., powerflow controller 1904).According to an exemplary embodiment, an electronic control unit mayhave a processing circuit, including a processing device and a memorydevice. Each electronic control unit may be responsible for managing oneor more vehicle systems. Vehicle systems include the engine,transmission, electromagnetic devices, other devices, or any combinationthereof that are capable of managing vehicle functions. In someembodiments, for example, engine and transmission control may becombined in a drive train control unit.

Vehicle controller 1902 and/or one of its component electronic controlunits may be configured to carry out processes required to control,monitor, and manage one or more devices in a vehicle. Vehicle controller1902 is shown to include powerflow controller 1904, brake controller1930, and airbag controller 1940. In FIG. 19A, vehicle controller 1902is shown to be broken to indicate that other controllers (for, e.g.,doors, emergency lights, sirens, radar, satellite communications, etc.)may be part of the vehicle controller. Vehicle controller 1902 includesa communications interface 1924 to vehicle systems 1950. In oneembodiment, communications interface 1924 is a vehicle systemscommunications interface. Communications interface 1924 can be orinclude wired or wireless interfaces (e.g., jacks, antennas,transmitters, receivers, transceivers, wire terminals, etc.) forconducting data communications with, e.g., engine 1952, electromagneticdevices 1954, 1956, or others vehicle systems via a direct connection.An exemplary embodiment of data communications between vehiclecontroller 1902 and vehicle system 1950 is shown in FIG. 19C. Vehiclecontroller 1902 and/or one of its component electronic control units(e.g., powerflow controller 1904) may be configured to carry out, e.g.,process 400 (FIG. 4), process 600 (FIG. 6), process 1000 (FIG. 10),process 1400 (FIG. 14), process 1500 (FIG. 15), process 1600 (FIG. 16),and other processes required to control the vehicle.

Vehicle controller 1902 includes powerflow controller 1904. Powerflowcontroller 1904 may be an electronic control unit responsible forcontrolling the systems of a vehicle drive train. Powerflow controller1904 may be configured to measure or receive input or feedback from oneor more vehicle systems and/or other electronic control units of vehiclecontroller 1902. Powerflow controller 1904 may be further configured tocompute and output commands to one or more drive train systems. Forexample, powerflow controller may control an engine 1952,electromagnetic devices EM1 (1954), EM2 (1956), transmission 1958, oneor more clutches 1960, throttle 1962, and shifter 1964. In otherembodiments, powerflow controller may control more, fewer, and differentvehicle systems.

Vehicle controller 1902 includes processing device 1906 and memorydevice 1908. In some embodiments, powerflow controller 1904 is amicrocontroller. In other embodiments, powerflow controller 1902 is amicroprocessor-based device and includes a microprocessor that executescontrol instructions stored in a memory. Processor 1906 can beimplemented as a general purpose processor, an application specificintegrated circuit (ASIC), one or more field programmable gate arrays(FPGAs), a group of processing components, or other suitable electronicprocessing components. Memory device 1908 (e.g., memory, memory unit,storage device, etc.) is one or more devices (e.g., RAM, ROM, Flashmemory, hard disk storage, etc.) for storing data and/or computer codefor completing or facilitating the various processes and modulesdescribed in the present application. Memory device 1908 may be orinclude volatile memory or non-volatile memory. Memory device 1908 mayinclude database components, object code components, script components,or any other type of information structure for supporting the variousactivities and information structures described in the presentapplication. According to an exemplary embodiment, memory device 1908 iscommunicably connected to processing device 1906.

Memory includes computer code for executing (e.g., by processing circuitand/or processor 1906) one or more processes described herein. Accordingto an exemplary embodiment, memory 1908 is divided into modules thatperform a particular function or control a particular vehicle system.Memory device 1908 includes engine control module 1910, EM1 commandmodule 1912, EM2 command module 1914, transmission control module 1916,clutch command module 1918, power calculation module 1920, and vehiclestatus module 1922. The modules are described in greater detail in thediscussion of FIG. 19B. According to an exemplary embodiment, one ormore vehicle systems 1950 may communicate via controller area network(CAN).

Referring to FIG. 19B, a more detailed block diagram of powerflowcontroller 1904 of FIG. 19A is shown, according to an exemplaryembodiment. As described in the discussion of FIG. 19A, powerflowcontroller 1904 includes a processing device 1906 and memory device1908. Memory device 1908 includes vehicle status module 1918. Vehiclestatus module may be configured to measure and/or receive data regardingthe operating status of the vehicle. Operating status may depend oninput from a vehicle operator. Operating status data includes wheelspeed 1985, shifter input 1987 (e.g., reverse, neutral, drive), brakeinput 1986, throttle input 1988 (received from, e.g., an acceleratorpedal sensor), and accessory loads 1989 (power required by, e.g., asteering pump). Vehicle status module 1922 may receive input from othermodules of memory 1908. In some embodiments, wheel speed may be receivedor measured by transmission control module and transmitted to vehiclestatus module 1922. In other embodiments, a wheel speed sensor of thevehicle may measure wheel speed and transmit the data to vehicle statusmodule 1922. Vehicle status module 1922 may transmit data regarding thevehicle (e.g., wheel speed) to other modules of memory 1908.

Memory device 1908 includes transmission control module 1916.Transmission control module 1916 may be configured to compute andtransmit commands for transmission 1958 (FIG. 19A). In particular,transmission control module 1916 may include instructions for computingand commanding configurations 1972. Configurations may includeoutput-coupled mode and input-coupled mode. Transmission control module1916 may command transmission configurations as described in thediscussions of FIGS. 6-8. Transmission control module may also includeplanetary gear set monitoring data 1973. Planetary gear set monitoringdata includes gear ratios and couplings of the components of theplanetary gear set. Transmission control module also includes monitoringdata from transmission input 1974 and output 1975. Input data 1974 mayinclude torque and speed from the engine and an electromagnetic deviceapplied to the transmission. Output data 1974 may include speed andtorque output of the transmission to the wheels of the vehicle.Transmission control module 1916 may receive input from other modules ofmemory 1908 (e.g., vehicle status module 1922). Transmission controlmodule 1916 may be further configured to receive feedback fromtransmission 1958. Feedback may include current configuration and outputspeed (i.e., speed delivered to the wheels of the vehicle). According toan exemplary embodiment, output speed may be used to compute the maximumpower deliverable by the drive train. Transmission control module 1916may transmit data regarding the transmission to other modules of memory1908, including clutch command module 1918, power calculation module1920, EM1 command module 1912, EM2 command module 1914, and enginecontrol module 1910, etc. According to an exemplary embodiment, clutchcommand module 1918 may receive input regarding transmissionconfiguration from transmission control module 1916 and issue clutchcommands as necessary.

Memory device 1908 includes clutch command module 1918. Clutch commandmodule 1918 may be configured to compute and transmit commands forclutches 1960 (FIG. 19A). Clutch system 1960 may include clutches C1, C2of FIG. 2. In particular, clutch command module 1972 may includeinstructions for commanding clutch C1 (1976) and clutch C2 (1977) to beengaged or disengaged. Controlling clutch C1 and clutch C2 to be engagedor disengaged may determine if the transmission is input-coupled oroutput-coupled. Clutch command module 1918 may be further configured tocontrol clutch C3 and clutch C4 (FIG. 2) to be engaged or disengaged.Clutch command module 1918 may receive input from other modules ofmemory 1908 (e.g., transmission control module 1916). According to anexemplary embodiment, clutch command module 1918 may receive inputregarding transmission configuration from transmission control module1916 and issue clutch commands as necessary. Clutch command module 1918may be further configured to receive feedback from clutches 1960.Feedback may include current configuration (e.g., engaged ordisengaged). Clutch command module 1918 may transmit data regardingclutch status to other modules of memory 1908.

Memory device 1908 includes engine control module 1910. Engine controlmodule 1910 may be configured to compute and transmit commands to engine1952 (FIG. 19A). In particular, engine control module 1910 may includeinstructions for computing and commanding engine speed 1970 and enginetorque 1971. Speed commands 1970 may be computed as described in thediscussion of FIG. 14. Engine control module 1910 may receive input fromother modules of memory 1908 (e.g., vehicle status module 1922). Enginecontrol module 1910 may be further configured to receive feedback fromengine system 1952. Feedback may include operating status (e.g., speed,torque, etc.). Engine control module 1910 may transmit data regardingengine torque and speed to other modules of memory 1908, including powercalculation module 1920, transmission control module 1916, EM1 commandmodule 1912, EM2 command module 1914, etc.

Memory device 1908 includes power calculation module 1920. Powercalculation module 1920 may be configured to compute the powerdeliverable (1979) by the drive train at a given vehicle speed, enginespeed, and transmission configuration. The power deliverable may becalculated as described in the discussion of FIG. 13. The calculatedpower deliverable may be used to determine the engine speed command andthe torque command, as described in FIGS. 14 and 16, respectively. Powercalculation module 1920 may be further configured to compute theelectrical power requested from the drive train (1981). The requestedelectrical power may be used to compute the torque command, as describedin FIG. 16. Power calculation module 1920 may also store constraints onthe drive train components. For example, power calculation module 1920may store speed constraints described in FIG. 17. Power calculationmodule 1910 may receive input from other modules of memory 1908 (e.g.,engine speed from engine control module 910, transmission output speedfrom transmission control module 1916, throttle input and accessoryloads from vehicle status module 1922, etc.). Power calculation module1920 may transmit data regarding power deliverable, requested electricalpower, and constraints to other modules of memory 1908. For example,power calculation module 1920 may transmit EM1 speed constraints toengine command module so, when EM1 speed approaches a threshold, theengine command module may command increased engine speed.

Memory device 1908 includes EM1 command module 1912 and EM2 commandmodule 1914. EM1 command module 1912 and EM2 command module 1914 may beconfigured to compute operating parameters for the electromagneticdevices. Operating parameters include operating mode 1984 (EM1), 1990(EM2) (e.g., voltage mode or torque mode), speed 1982 (EM1), 1988 (EM2),and torque 1983 (EM1), 1989 (EM2). According to an exemplary embodiment,a CAN message may command a particular operating mode to EM1 and EM2.This may advantageously allow for simultaneous switching of EM1 and EM2between voltage and torque modes. A torque command for theelectromagnetic device in torque mode may be calculated as described inthe discussion of FIG. 16. EM1 command module 1912 and EM2 commandmodule 1914 may receive input from other modules of memory 1908 (e.g.,vehicle speed from vehicle status module 1922, electrical power requiredfrom power calculation module 1920, etc.). EM1 command module 1912 andEM2 command module 1914 may also receive feedback from EM1 system 1954and EM2 system 1956. Feedback may include current torque and speed ofthe particular electromagnetic device. EM1 command module 1912 and EM2command module 1914 may transmit data regarding operating parameters toother modules of memory 1908.

In some embodiments, EM1 command module 1912 and EM2 command module 1914may be configured to operate EM1 and EM2 within specified speeds (asdescribed in FIG. 17). For example, EM1 command module may transmit datato power calculation module 1920 or engine control module 1910 when EM1speeds approach an upper threshold. Engine control module may command ahigher engine speed in order to lower EM1 speed. In some embodiments,EM1 and EM2 may be connected by an electrical power link (e.g., DC bus).The electromagnetic device in voltage mode may be configured to maintaina specified voltage on the DC bus. Powerflow controller 1904 may beconfigured to received voltage feedback from the DC bus between EM1 andEM2. Based on the voltage feedback, EM1 command module and/or EM2command module may increase or decrease torque or speed. This may berequired to maintain power balance with the other electromagnetic deviceas described in the discussion of FIG. 15.

Referring to FIG. 19C, a detailed diagram of communications betweenpowerflow controller 1904 of FIG. 19A and certain vehicle systems isshown, according to an exemplary embodiment. Communications may includeinput and/or feedback received by powerflow controller 1904 from vehiclesystems 1950. Communications may also include commands that aretransmitted by powerflow controller 1904 to vehicle systems 1950. Inputand feedback data are used to compute commands for, e.g., engine 1952,clutches 1918, EM1 1954, and EM2 1956. Powerflow controller 1904 may beconfigured to communicate with vehicle systems 1950 via communicationsinterface 1924 (FIG. 19A).

Powerflow controller 1904 may receive data regarding the operatingstatus of the vehicle. Operating status data is described in step 402 ofprocess 400 (FIG. 4). Powerflow controller may receive load data fromaccessories 1990 (i.e., power required to operate an accessory, and,thus, power unavailable for vehicle propulsion). Powerflow controllermay receive input from brakes 1968 (e.g., proportion engaged), shifter1964 (e.g., reverse, neutral, drive), and throttle 1968 (e.g., inputproportion). Powerflow controller may also receive transmission outputspeed from transmission 1958. Data received from the vehicle systems1950 may be used to compute transmission configuration (output-coupledor input-coupled), engine speed, EM1 and EM2 operating modes (torque orvoltage), EM1 and EM2 speeds and/or torques, etc.

Powerflow controller 1904 may be configured to communicate with clutches1918. Clutches 1918 may transmit current status (engaged or disengaged)to powerflow controller 1904. Based on the determination of transmissionconfiguration (output-coupled or input-coupled), powerflow controllermay command clutch C1 (1976) and/or clutch C2 (1977) to be engaged ordisengaged.

Powerflow controller 1904 may be configured to communicate with engine1952. Engine 1952 may transmit feedback regarding current operatingconditions (e.g., torque and speed) to powerflow controller 1904. Basedon the computation of optimum engine speed, powerflow controller may beconfigured to transmit engine speed commands to engine 1952.

Powerflow controller 1904 may be configured to communicate withelectromagnetic devices EM1 (1954) and EM2 (1956). EM1 and EM2 may beconfigured to provide feedback (e.g., current torque and speed) topowerflow controller 1904. Based on the computation of electrical powerrequested, powerflow controller 1904 may transmit torque and voltagecommands to EM1 and EM2. Powerflow controller 1904 may also beconfigured to receive voltage feedback from the DC bus between EM1 andEM2. Powerflow controller may use the voltage feedback to determineappropriate commands for EM1 and EM2 so that EM1 and EM2 operate inpower balance.

Throughout the specification, numerous advantages of exemplaryembodiments have been identified. It will be understood of course thatit is possible to employ the teachings herein without necessarilyachieving the same advantages. Additionally, although many features havebeen described in the context of a vehicle controller comprisingmultiple controllers and/or modules, it will be appreciated that suchfeatures could also be implemented in the context of other hardwareconfigurations. Further, although various figures depict a series ofsteps which are performed sequentially, the steps shown in such figuresgenerally need not be performed in any particular order. For example, inpractice, modular programming techniques are used and therefore some ofthe steps may be performed essentially simultaneously. Additionally,some steps shown may be performed repetitively with particular ones ofthe steps being performed more frequently than others. Alternatively, itmay be desirable in some situations to perform steps in a differentorder than shown. The teachings and methods herein may be applied tocontrol of drive trains for a variety of vehicles, including cars,trucks, motorcycles, trains, ships, boats, aircraft, etc. The teachingsand methods may have consumer, commercial, industrial, military, andother uses. Many other changes and modifications may be made to thepresent invention without departing from the spirit thereof.

1. A method of operating a first motor/generator and a secondmotor/generator in a vehicle drive, the first motor/generatorelectrically coupled to the second motor/generator by a DC bus and thevehicle drive configured to propel a vehicle, the method comprising:operating the vehicle drive in a first operating mode by: operating thefirst motor/generator as a generator, wherein the first motor/generatorprovides electrical power to the DC bus to maintain a first voltage onthe DC bus when operated as a generator, and wherein the firstmotor/generator provides all of an electrical power required by thesecond motor/generator and an electrical power required to offsetelectrical power losses; and operating the second motor/generator as amotor, wherein the second motor/generator consumes electrical power fromthe DC bus when operated as a motor, and wherein a sum of the electricalpower provided by the first motor/generator, the electrical powerlosses, and the electrical power consumed by the second motor/generatoris zero; wherein the first motor/generator provides electrical power tothe DC bus and the second motor/generator consumes electrical power fromthe DC bus without doing either of (a) providing electrical power to anenergy storage device or (b) consuming electrical power from an energystorage device; and operating the vehicle drive in a second operatingmode by: operating both the first motor/generator as a generator and thesecond motor/generator as a generator when a first power generationcapability associated with the first motor/generator is below a firstthreshold level, wherein the first motor/generator and the secondmotor/generator provide electrical power to the DC bus to maintain asecond voltage on the DC bus when operated as generators, and whereinthe first motor/generator and the second motor/generator provide all ofthe electrical power required to offset electrical power losses; whereinthe first motor/generator and the second motor/generator provideelectrical power to the DC bus without doing either of (a) providingelectrical power to an energy storage device or (b) consuming electricalpower from an energy storage device.
 2. The method of claim 1, furthercomprising operating the vehicle drive in a third operating mode by:operating the second motor/generator as a generator, wherein the secondmotor/generator provides electrical power to the DC bus to maintain athird voltage on the DC bus when operated as a generator, and whereinthe second motor/generator provides all of an electrical power requiredby the first motor/generator and an electrical power required to offsetelectrical power losses; and operating the first motor/generator as amotor when a second power generation capability associated with thesecond motor/generator is greater than a second threshold level, whereinthe first motor/generator consumes electrical power from the DC bus whenoperated as a motor, and wherein the sum of the electrical powerprovided by the second motor/generator, the electrical power losses, andthe electrical power consumed by the first motor/generator is zero,wherein the second motor/generator provides electrical power to the DCbus and the first motor/generator consumes electrical power from the DCbus without doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.
 3. The method of claim 2, wherein the second threshold level isequal to the first threshold level.
 4. The method of claim 2, whereinthe first threshold level and the second threshold level are related tothe electrical power losses.
 5. The method of claim 2, wherein at leastone of the first threshold level and the second threshold level is equalto the electrical power losses.
 6. The method of claim 2, furthercomprising operating the vehicle drive in a fourth operating mode by:operating at least one of the first motor/generator as a generator andthe second motor/generator as a generator, wherein the at least one ofthe first motor/generator and the second motor/generator provides atleast a portion of an electrical power required by the vehicle and atleast a portion of the electrical power required to offset electricalpower losses; wherein the at least one of the first motor/generator andthe second motor/generator provide electrical power to the DC buswithout doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.
 7. The method of claim 2, wherein the first motor/generatormaintains a voltage on the DC bus when a speed of the firstmotor/generator is above a threshold speed, and wherein the secondmotor/generator maintains a voltage on the DC bus when the speed of thefirst motor/generator is below the threshold speed.
 8. The method ofclaim 7, further comprising transmitting a controller area networkmessage with a controller to the first motor/generator and the secondmotor/generator, wherein the controller area network message specifieswhich motor/generator maintains a voltage on the DC bus.
 9. A method ofoperating a first motor/generator and a second motor/generator in avehicle drive, the first motor/generator electrically coupled to thesecond motor/generator by a DC bus and the vehicle drive configured topropel a vehicle, the method comprising: operating the vehicle drive ina first operating mode by: operating the first motor/generator as agenerator, wherein the first motor/generator provides electrical powerto the DC bus to maintain a first voltage on the DC bus when operated asa generator, and wherein the first motor/generator provides all of anelectrical power required by the second motor/generator and anelectrical power required to offset electrical power losses; andoperating the second motor/generator as a motor, wherein the secondmotor/generator consumes electrical power from the DC bus when operatedas a motor, and wherein a sum of the electrical power provided by thefirst motor/generator, the electrical power losses, and the electricalpower consumed by the second motor/generator is zero; wherein the firstmotor/generator provides electrical power to the DC bus and the secondmotor/generator consumes electrical power from the DC bus without doingeither of (a) providing electrical power to an energy storage device or(b) consuming electrical power from an energy storage device; andoperating the vehicle drive in a second operating mode by: operatingboth the first motor/generator as a generator and the secondmotor/generator as a generator when the electrical power losses aregreater than the electrical power provided by the first motor/generator,wherein the first motor/generator and the second motor/generator provideelectrical power to the DC bus to maintain a second voltage on the DCbus when operated as generators, and wherein the first motor/generatorand the second motor/generator provide all of the electrical powerrequired to offset electrical power losses; wherein the firstmotor/generator and the second motor/generator provide electrical powerto the DC bus without doing either of (a) providing electrical power toan energy storage device or (b) consuming electrical power from anenergy storage device.
 10. The method of claim 9, further comprisingoperating the vehicle drive in a third operating mode by: operating thesecond motor/generator as a generator, wherein the secondmotor/generator provides electrical power to the DC bus to maintain athird voltage on the DC bus when operated as a generator, and whereinthe second motor/generator provides all of an electrical power requiredby the first motor/generator and an electrical power required to offsetelectrical power losses; and operating the first motor/generator as amotor when the electrical power provided by the second motor/generatoris greater than the electrical power losses, wherein the firstmotor/generator consumes electrical power from the DC bus when operatedas a motor, and wherein the sum of the electrical power provided by thesecond motor/generator, the electrical power losses, and the electricalpower consumed by the first motor/generator is zero, wherein the secondmotor/generator provides electrical power to the DC bus and the firstmotor/generator consumes electrical power from the DC bus without doingeither of (a) providing electrical power to an energy storage device or(b) consuming electrical power from an energy storage device.
 11. Themethod of claim 10, further comprising operating the vehicle drive in afourth operating mode by: operating at least one of the firstmotor/generator as a generator and the second motor/generator as agenerator, wherein the at least one of the first motor/generator and thesecond motor/generator provides at least a portion of an electricalpower required by the vehicle and at least a portion of the electricalpower required to offset electrical power losses; wherein the at leastone of the first motor/generator and the second motor/generator provideelectrical power to the DC bus without doing either of (a) providingelectrical power to an energy storage device or (b) consuming electricalpower from an energy storage device.
 12. The method of claim 11, whereinthe first motor/generator maintains a voltage on the DC bus when a speedof the first motor/generator is above a threshold speed, and wherein thesecond motor/generator maintains a voltage on the DC bus when the speedof the first motor/generator is below the threshold speed.
 13. Themethod of claim 12, further comprising transmitting a controller areanetwork message with a controller to the first motor/generator and thesecond motor/generator, wherein the controller area network messagespecifies which motor/generator maintains a voltage on the DC bus.
 14. Asystem for operating a first motor/generator and a secondmotor/generator in a vehicle drive, the first motor/generatorelectrically coupled to the second motor/generator by a DC bus and thevehicle drive configured to propel a vehicle, the system comprising aprocessing circuit configured to: operate the vehicle drive in a firstoperating mode by: operating the first motor/generator as a generator,wherein the first motor/generator provides electrical power to the DCbus to maintain a first voltage on the DC bus when operated as agenerator, and wherein the first motor/generator provides all of anelectrical power required by the second motor/generator and anelectrical power required to offset electrical power losses; andoperating the second motor/generator as a motor, wherein the secondmotor/generator consumes electrical power from the DC bus when operatedas a motor, and wherein a sum of the electrical power provided by thefirst motor/generator, the electrical power losses, and the electricalpower consumed by the second motor/generator is zero; wherein the firstmotor/generator provides electrical power to the DC bus and the secondmotor/generator consumes electrical power from the DC bus without doingeither of (a) providing electrical power to an energy storage device or(b) consuming electrical power from an energy storage device; andoperate the vehicle drive in a second operating mode by: operating boththe first motor/generator as a generator and the second motor/generatoras a generator when a first power generation capability associated withthe first motor/generator is below a first threshold level, wherein thefirst motor/generator and the second motor/generator provide electricalpower to the DC bus to maintain a second voltage on the DC bus whenoperated as generators, and wherein the first motor/generator and thesecond motor/generator provide all of the electrical power required tooffset electrical power losses; wherein the first motor/generator andthe second motor/generator provide electrical power to the DC buswithout doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.
 15. The system of claim 14, wherein the processing circuit isconfigured to operate the vehicle drive in a third operating mode by:operating the second motor/generator as a generator, wherein the secondmotor/generator provides electrical power to the DC bus to maintain athird voltage on the DC bus when operated as a generator, and whereinthe second motor/generator provides all of an electrical power requiredby the first motor/generator and an electrical power required to offsetelectrical power losses; and operating the first motor/generator as amotor when a second power generation capability associated with thesecond motor/generator is greater than a second threshold level, whereinthe first motor/generator consumes electrical power from the DC bus whenoperated as a motor, and wherein the sum of the electrical powerprovided by the second motor/generator, the electrical power losses, andthe electrical power consumed by the first motor/generator is zero,wherein the second motor/generator provides electrical power to the DCbus and the first motor/generator consumes electrical power from the DCbus without doing either of (a) providing electrical power to an energystorage device or (b) consuming electrical power from an energy storagedevice.
 16. The system of claim 15, wherein the second threshold levelis equal to the first threshold level.
 17. The system of claim 15,wherein the first threshold level and the second threshold level arerelated to the electrical power losses.
 18. The system of claim 15,wherein at least one of the first threshold level and the secondthreshold level is equal to the electrical power losses.
 19. The systemof claim 15, wherein the processing circuit is configured to operate thevehicle drive in a fourth operating mode by: operating at least one ofthe first motor/generator as a generator and the second motor/generatoras a generator, wherein the at least one of the first motor/generatorand the second motor/generator provides at least a portion of anelectrical power required by the vehicle and at least a portion of theelectrical power required to offset electrical power losses; wherein theat least one of the first motor/generator and the second motor/generatorprovide electrical power to the DC bus without doing either of (a)providing electrical power to an energy storage device or (b) consumingelectrical power from an energy storage device.
 20. The system of claim15, wherein the first motor/generator maintains a voltage on the DC buswhen a speed of the first motor/generator is above a threshold speed,and wherein the second motor/generator maintains a voltage on the DC buswhen the speed of the first motor/generator is below the thresholdspeed.